# libconfig

A Library For Processing Structured Configuration Files
Version 1.8.2
14 Dec 2025
Mark A. Lindner

Next: Introduction [Contents][Index]

# libconfig

## Table of Contents

- 1 Introduction
  - 1.1 Why Another Configuration File Library?
  - 1.2 Using the Library from a C Program
  - 1.3 Using the Library from a C++ Program
  - 1.4 Multithreading Issues
  - 1.5 Internationalization Issues
  - 1.6 Compiling Using pkg-config
  - 1.7 Version Test Macros
- 2 Configuration Files
  - 2.1 Settings
  - 2.2 Groups
  - 2.3 Arrays
  - 2.4 Lists
  - 2.5 Integer Values
  - 2.6 64-bit Integer Values
  - 2.7 Floating Point Values
  - 2.8 Boolean Values
  - 2.9 String Values
  - 2.10 Comments
  - 2.11 Include Directives
- 3 The C API
- 4 The C++ API
- 5 Example Programs
- 6 Other Bindings and Implementations
  - 6.1 Bourne Shell
  - 6.2 D
  - 6.3 Haskell
  - 6.4 Java
  - 6.5 Lisp
  - 6.6 Perl
  - 6.7 Python
  - 6.8 Ruby
  - 6.9 Rust
- Appendix A License
- Appendix B Configuration File Grammar
- Function Index
- Type Index
- Concept Index

Next: Configuration Files, Previous: libconfig, Up: libconfig [Contents][Index]

## 1 Introduction

Libconfig is a library for reading, manipulating, and writing structured configuration files. The library features a fully reentrant parser and includes bindings for both the C and C++ programming languages.

The library runs on modern POSIX-compilant systems, such as GNU/Linux, FreeBSD, OpenBSD, and MacOS (Darwin), as well as on Microsoft Windows 2000/XP and later (with either Microsoft Visual Studio 2005 or later, or the GNU toolchain via the MinGW environment).

Next: Using the Library from a C Program, Up: Introduction [Contents][Index]

### 1.1 Why Another Configuration File Library?

There are several open-source configuration file libraries available as of this writing. This library was written because each of those libraries falls short in one or more ways. The main features of libconfig that set it apart from the other libraries are:

- A fully reentrant parser. Independent configurations can be parsed in concurrent threads at the same time.
- Both C and C++ bindings, as well as hooks to allow for the creation of wrappers in other languages.
- A simple, structured configuration file format that is more readable and compact than XML and more flexible than the obsolete but prevalent Windows “INI” file format.
- A low-footprint implementation (just 37K for the C library and 76K for the C++ library) that is suitable for memory-constrained systems.
- Proper documentation.

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### 1.2 Using the Library from a C Program

To use the library from C code, include the following preprocessor directive in your source files:

    #include <libconfig.h>

To link with the library, specify ‘`-lconfig`’ as an argument to the linker.

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### 1.3 Using the Library from a C++ Program

To use the library from C++, include the following preprocessor directive in your source files:

    #include <libconfig.h++>

Or, alternatively:

    #include <libconfig.hh>

The C++ API classes are defined in the namespace ‘`libconfig`’, hence the following statement may optionally be used:

    using namespace libconfig;

To link with the library, specify ‘`-lconfig++`’ as an argument to the linker.

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### 1.4 Multithreading Issues

Libconfig is fully reentrant; the functions in the library do not make use of global variables and do not maintain state between successive calls. Therefore two independent configurations may be safely manipulated concurrently by two distinct threads.

Libconfig is not thread-safe. The library is not aware of the presence of threads and knows nothing about the host system’s threading model. Therefore, if an instance of a configuration is to be accessed from multiple threads, it must be suitably protected by synchronization mechanisms like read-write locks or mutexes; the standard rules for safe multithreaded access to shared data must be observed.

Libconfig is not async-safe. Calls should not be made into the library from signal handlers, because some of the C library routines that it uses may not be async-safe.

Libconfig is not guaranteed to be cancel-safe. Since it is not aware of the host system’s threading model, the library does not contain any thread cancellation points. In most cases this will not be an issue for multithreaded programs. However, be aware that some of the routines in the library (namely those that read/write configurations from/to files or streams) perform I/O using C library routines which may potentially block; whether or not these C library routines are cancel-safe depends on the host system.

Next: Compiling Using pkg-config, Previous: Multithreading Issues, Up: Introduction [Contents][Index]

### 1.5 Internationalization Issues

Libconfig does not natively support Unicode configuration files, but string values may contain Unicode text encoded in UTF-8; such strings will be treated as ordinary 8-bit ASCII text by the library. It is the responsibility of the calling program to perform the necessary conversions to/from wide (`wchar_t`) strings using the wide string conversion functions such as `mbsrtowcs()` and `wcsrtombs()` or the `iconv()` function of the libiconv library.

The textual representation of a floating point value varies by locale. However, the libconfig grammar specifies that floating point values are represented using a period (‘.’) as the radix symbol; this is consistent with the grammar of most programming languages. When a configuration is read in or written out, libconfig temporarily changes the `LC_NUMERIC` category of the locale of the calling thread to the “C” locale to ensure consistent handling of floating point values regardless of the locale(s) in use by the calling program.

Note that the MinGW environment does not (as of this writing) provide functions for changing the locale of the calling thread. Therefore, when using libconfig in that environment, the calling program is responsible for changing the `LC_NUMERIC` category of the locale to the "C" locale before reading or writing a configuration.

Next: Version Test Macros, Previous: Internationalization Issues, Up: Introduction [Contents][Index]

### 1.6 Compiling Using pkg-config

On UNIX systems you can use the pkg-config utility (version 0.20 or later) to automatically select the appropriate compiler and linker switches for libconfig. Ensure that the environment variable `PKG_CONFIG_PATH` contains the absolute path to the `lib/pkgconfig` subdirectory of the libconfig installation. Then, you can compile and link C programs with libconfig as follows:

    gcc `pkg-config --cflags libconfig` myprogram.c -o myprogram \
        `pkg-config --libs libconfig`

And similarly, for C++ programs:

    g++ `pkg-config --cflags libconfig++` myprogram.cpp -o myprogram \
        `pkg-config --libs libconfig++`

Note the backticks in the above examples.

When using autoconf, the `PKG_CHECK_MODULES` m4 macro may be used to check for the presence of a given version of libconfig, and set the appropriate Makefile variables automatically. For example:

    PKG_CHECK_MODULES([LIBCONFIGXX], [libconfig++ >= 1.4],,
      AC_MSG_ERROR([libconfig++ 1.4 or newer not found.])
    )

In the above example, if libconfig++ version 1.4 or newer is found, the Makefile variables `LIBCONFIGXX_LIBS` and `LIBCONFIGXX_CFLAGS` will be set to the appropriate compiler and linker flags for compiling with libconfig, and if it is not found, the configure script will abort with an error to that effect.

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### 1.7 Version Test Macros

The `libconfig.h` header declares the following macros:

Macro: LIBCONFIG_VER_MAJOR ¶
Macro: LIBCONFIG_VER_MINOR ¶
Macro: LIBCONFIG_VER_REVISION ¶

  These macros represent the major version, minor version, and revision of the libconfig library. For example, in libconfig 1.4 these are defined as ‘`1`’, ‘`4`’, and ‘`0`’, respectively. These macros can be used in preprocessor directives to determine which libconfig features and/or APIs are present. For example:

      #if (((LIBCONFIG_VER_MAJOR == 1) && (LIBCONFIG_VER_MINOR >= 4)) \
           || (LIBCONFIG_VER_MAJOR > 1))
        /* use features present in libconfig 1.4 and later */
      #endif

  These macros were introduced in libconfig 1.4.

Similarly, the `libconfig.h++` header declares the following macros:

Macro: LIBCONFIGXX_VER_MAJOR ¶
Macro: LIBCONFIGXX_VER_MINOR ¶
Macro: LIBCONFIGXX_VER_REVISION ¶

  These macros represent the major version, minor version, and revision of the libconfig++ library.

Next: The C API, Previous: Introduction, Up: libconfig [Contents][Index]

## 2 Configuration Files

Libconfig supports structured, hierarchical configurations. These configurations can be read from and written to files and manipulated in memory.

A configuration consists of a group of settings, which associate names with values. A value can be one of the following:

- A scalar value: integer, 64-bit integer, floating-point number, boolean, or string
- An array, which is a sequence of scalar values, all of which must have the same type
- A group, which is a collection of settings
- A list, which is a sequence of values of any type, including other lists

Consider the following configuration file for a hypothetical GUI application, which illustrates all of the elements of the configuration file grammar.

    # Example application configuration file

    version = "1.0";

    application:
    {
      window:
      {
        title = "My Application";
        size = { w = 640; h = 480; };
        pos = { x = 350; y = 250; };
      };

      list = ( ( "abc", 123, true ), 1.234, ( /* an empty list */ ) );

      books = ( { title  = "Treasure Island";
                  author = "Robert Louis Stevenson";
                  price  = 29.95;
                  qty    = 5; },
                { title  = "Snow Crash";
                  author = "Neal Stephenson";
                  price  = 9.99;
                  qty    = 8; } );

      constants:
      {
        pi = 3.141592654;
        bigint = 9223372036854775807L;
        columns = [ "Last Name", "First Name", "MI" ];
        bitmask1 = 0x1FC3; // hex
        bitmask2 = 0b1011; // binary
        umask = 0o755; // octal
      };
    };

Settings can be uniquely identified within the configuration by a path. The path is a dot-separated sequence of names, beginning at a top-level group and ending at the setting itself. Each name in the path is the name of a setting; if the setting has no name because it is an element in a list or array, an integer index in square brackets can be used as the name.

For example, in our hypothetical configuration file, the path to the `x` setting is `application.window.pos.x`; the path to the `version` setting is simply `version`; and the path to the `title` setting of the second book in the `books` list is `application.books.[1].title`.

The datatype of a value is determined from the format of the value itself. If the value is enclosed in double quotes, it is treated as a string. If it looks like an integer or floating point number, it is treated as such. If it is one of the values `TRUE`, `true`, `FALSE`, or `false` (or any other mixed-case version of those tokens, e.g., `True` or `FaLsE`), it is treated as a boolean. If it consists of a comma-separated list of values enclosed in square brackets, it is treated as an array. And if it consists of a comma-separated list of values enclosed in parentheses, it is treated as a list. Any value which does not meet any of these criteria is considered invalid and results in a parse error.

All names are case-sensitive. They may consist only of alphanumeric characters, dashes (‘`-`’), underscores (‘`_`’), and asterisks (‘`*`’), and must begin with a letter or asterisk. No other characters are allowed.

In C and C++, integer, 64-bit integer, floating point, and string values are mapped to the native types `int`, `long long`, `double`, and `const char *`, respectively. The boolean type is mapped to `int` in C and `bool` in C++.

The following sections describe the elements of the configuration file grammar in additional detail.

Next: Groups, Up: Configuration Files [Contents][Index]

### 2.1 Settings

A setting has the form:

name = value ;

or:

name : value ;

The trailing semicolon is optional. Whitespace is not significant.

The value may be a scalar value, an array, a group, or a list.

Next: Arrays, Previous: Settings, Up: Configuration Files [Contents][Index]

### 2.2 Groups

A group has the form:

{ settings ... }

Groups can contain any number of settings, but each setting must have a unique name within the group.

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### 2.3 Arrays

An array has the form:

[ value, value ... ]

An array may have zero or more elements, but the elements must all be scalar values of the same type.

The last element in an array may be followed by a comma, which will be ignored.

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### 2.4 Lists

A list has the form:

( value, value ... )

A list may have zero or more elements, each of which can be a scalar value, an array, a group, or another list.

The last element in a list may be followed by a comma, which will be ignored.

Next: 64-bit Integer Values, Previous: Lists, Up: Configuration Files [Contents][Index]

### 2.5 Integer Values

Integers can be represented in four ways:

- As a series of one or more decimal digits (‘`0`’ - ‘`9`’), with an optional leading sign character (‘`+`’ or ‘`-`’).
- As a binary value consisting of the characters ‘`0b`’ followed by a series of one or more binary digits (‘`0`’ - ‘`1`’).
- As an octal value consisting of the characters ‘`0o`’ or ‘`0q`’ followed by a series of one or more octal digits (‘`0`’ - ‘`7`’). (Since version 1.8.1; prior versions of the library supported the old octal format of a single leading ‘`0`’, which is ambiguous.)
- As a hexadecimal value consisting of the characters ‘`0x`’ followed by a series of one or more hexadecimal digits (‘`0`’ - ‘`9`’, ‘`A`’ - ‘`F`’, ‘`a`’ - ‘`f`’).

Next: Floating Point Values, Previous: Integer Values, Up: Configuration Files [Contents][Index]

### 2.6 64-bit Integer Values

Long long (64-bit) integers are represented identically to integers, except that an ‘L’ character is appended to indicate a 64-bit value. For example, ‘`0L`’ indicates a 64-bit integer value 0. As of version 1.5 of the library, the trailing ‘L’ is optional; if the integer value exceeds the range of a 32-bit integer, it will automatically be interpreted as a 64-bit integer.

As of version 1.8.1 of the library, this behavior also applies to integers expressed in binary (base 2), octal (base 8), and hexadecimal (base 16). A binary value with 32 or less digits and no trailing ‘L’ will always be parsed as a 32-bit integer, while a binary value with 33 to 64 digits or with a trailing ‘L’ will always be parsed as a 64-bit integer. Similarly, an octal value with 10 or less digits and no trailing ‘L’ will always be parsed as a 32-bit integer, while an octal value with 11 to 21 digits or with a trailing ‘L’ will always be parsed as a 64-bit integer. And finally, a hexadecimal value with 8 or less digits and no trailing ‘L’ will always be parsed as a 32-bit integer, while a hexadecimal value with 9 to 16 digits or with a trailing ‘L’ will always be parsed as a 64-bit integer.

The integer and 64-bit integer setting types are interchangeable to the extent that a conversion between the corresponding native types would not result in an overflow or underflow. For example, a long long value can be written to a setting that has an integer type, if that value is within the range of an int. This rule applies to every API function or method that reads a value from or writes a value to a setting: if the type conversion would not result in an overflow or underflow, then the call will succeed, and otherwise it will fail. This behavior was not well-defined prior to version 1.7 of the library.

Next: Boolean Values, Previous: 64-bit Integer Values, Up: Configuration Files [Contents][Index]

### 2.7 Floating Point Values

Floating point values consist of a series of one or more digits, one decimal point, an optional leading sign character (‘`+`’ or ‘`-`’), and an optional exponent. An exponent consists of the letter ‘`E`’ or ‘`e`’, an optional sign character, and a series of one or more digits.

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### 2.8 Boolean Values

Boolean values may have one of the following values: ‘`true`’, ‘`false`’, or any mixed-case variation thereof.

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### 2.9 String Values

String values consist of arbitrary text delimited by double quotes. Literal double quotes can be escaped by preceding them with a backslash: ‘`\"`’. The escape sequences ‘`\\`’, ‘`\f`’, ‘`\n`’, ‘`\r`’, ‘`\a`’, ‘`\b`’, ‘`\v`’ and ‘`\t`’ are also recognized, and have the usual meaning.

In addition, the ‘`\x`’ escape sequence is supported; this sequence must be followed by exactly two hexadecimal digits, which represent an 8-bit ASCII value. For example, ‘`\xFF`’ represents the character with ASCII code 0xFF.

No other escape sequences are currently supported.

Adjacent strings are automatically concatenated, as in C/C++ source code. This is useful for formatting very long strings as sequences of shorter strings. For example, the following constructs are equivalent:

- `"The quick brown fox jumped over the lazy dog."`
- `"The quick brown fox"`
  `" jumped over the lazy dog."`
- `"The quick" /* comment */ " brown fox " // another comment`
  `"jumped over the lazy dog."`

Next: Include Directives, Previous: String Values, Up: Configuration Files [Contents][Index]

### 2.10 Comments

Three types of comments are allowed within a configuration:

- Script-style comments. All text beginning with a ‘`#`’ character to the end of the line is ignored.
- C-style comments. All text, including line breaks, between a starting ‘`/*`’ sequence and an ending ‘`*/`’ sequence is ignored.
- C++-style comments. All text beginning with a ‘`//`’ sequence to the end of the line is ignored.

As expected, comment delimiters appearing within quoted strings are treated as literal text.

Comments are ignored when the configuration is read in, so they are not treated as part of the configuration. Therefore if the configuration is written back out to a stream, any comments that were present in the original configuration will be lost.

Previous: Comments, Up: Configuration Files [Contents][Index]

### 2.11 Include Directives

A configuration file may “include” the contents of other files using an include directive. This directive has the effect of inlining the contents of the named file(s) at the point of inclusion.

An include directive must appear on its own line in the input. It has the form:

@include "path"

The interpretation of path depends on the currently registered include function. The default include function prepends the include directory, if any, to path, and then interprets the result as a single, literal file path. The application may supply its own include function which does variable substitution, wildcard expansion, or other transformations, returning a list of zero or more paths to files whose contents should be inlined at the point of inclusion.

Any backslashes or double quotes in the path must be escaped as ‘`\\`’ and ‘`\"`’, respectively.

For example, consider the following two configuration files:

    # file: quote.cfg
    quote = "Criticism may not be agreeable, but it is necessary."
            " It fulfils the same function as pain in the human"
            " body. It calls attention to an unhealthy state of"
            " things.\n"
            "\t--Winston Churchill";

    # file: test.cfg
    info: {
      name = "Winston Churchill";
      @include "quote.cfg"
      country = "UK";
    };

The resulting configuration will be equivalent to one in which the contents of the file ‘`quote.cfg`’ appeared at the point where the include directive is placed.

Include files may be nested to a maximum of 10 levels; exceeding this limit results in a parse error.

When the path argument to an @include directive is a relative path, then it will be interpreted as being relative to the include directory that has been been set by means of `config_set_include_dir()`. If no include directory has been set, then it will be taken as being relative to the program’s current working directory.

Like comments, include directives are not part of the configuration file syntax. They are processed before the configuration itself is parsed. Therefore, they are not preserved when the configuration is written back out to a stream. There is presently no support for programmatically inserting include directives into a configuration.

Next: The C++ API, Previous: Configuration Files, Up: libconfig [Contents][Index]

## 3 The C API

This chapter describes the C library API. The type config_t represents a configuration, and the type config_setting_t represents a configuration setting.

The boolean values `CONFIG_TRUE` and `CONFIG_FALSE` are macros defined as `(1)` and `(0)`, respectively.

Function: void config_init (config_t * config) ¶
Function: void config_destroy (config_t * config) ¶

  These functions initialize and destroy the configuration object config.

  `config_init()` initializes the config_t structure pointed to by config as a new, empty configuration.

  `config_destroy()` destroys the configuration config, deallocating all memory associated with the configuration, but does not attempt to deallocate the config_t structure itself.

Function: void config_clear (config_t * config) ¶

  Since v1.7

  This function clears the configuration config. All child settings of the root setting are recursively destroyed. All other attributes of the configuration are left unchanged.

Function: int config_read (config_t * config, FILE * stream) ¶

  This function reads and parses a configuration from the given stream into the configuration object config. It returns `CONFIG_TRUE` on success, or `CONFIG_FALSE` on failure; the `config_error_text()`, `config_error_file()`, `config_error_line()`, and `config_error_type()` functions, described below, can be used to obtain information about the error.

Function: int config_read_file (config_t * config, const char * filename) ¶

  This function reads and parses a configuration from the file named filename into the configuration object config. It returns `CONFIG_TRUE` on success, or `CONFIG_FALSE` on failure; the `config_error_text()` and `config_error_line()` functions, described below, can be used to obtain information about the error.

Function: int config_read_string (config_t * config, const char * str) ¶

  This function reads and parses a configuration from the string str into the configuration object config. It returns `CONFIG_TRUE` on success, or `CONFIG_FALSE` on failure; the `config_error_text()` and `config_error_line()` functions, described below, can be used to obtain information about the error.

Function: void config_write (const config_t * config, FILE * stream) ¶

  This function writes the configuration config to the given stream.

Function: int config_write_file (config_t * config, const char * filename) ¶

  This function writes the configuration config to the file named filename. It returns `CONFIG_TRUE` on success, or `CONFIG_FALSE` on failure.

Function: const char * config_error_text (const config_t * config) ¶
Function: const char * config_error_file (const config_t * config) ¶
Function: int config_error_line (const config_t * config) ¶

  These functions, which are implemented as macros, return the text, filename, and line number of the parse error, if one occurred during a call to `config_read()`, `config_read_string()`, or `config_read_file()`. Storage for the strings returned by `config_error_text()` and `config_error_file()` are managed by the library and released automatically when the configuration is destroyed; these strings must not be freed by the caller. If the error occurred in text that was read from a string or stream, `config_error_file()` will return NULL.

Function: config_error_t config_error_type (const config_t * config) ¶

  This function, which is implemented as a macro, returns the type of error that occurred during the last call to one of the read or write functions. The config_error_t type is an enumeration with the following values: `CONFIG_ERR_NONE`, `CONFIG_ERR_FILE_IO`, `CONFIG_ERR_PARSE`. These represent success, a file I/O error, and a parsing error, respectively.

Function: void config_set_fatal_error_func (config_fatal_error_fn_t func) ¶

  Since v1.7.4

  Specifies the function func to call when a fatal error is encountered. If func is `NULL`, the default fatal error handler function will be reinstated.

  The type config_fatal_error_fn_t is a type alias for a function whose signature is:

  Function: void func (const char *message) ¶

    The function receives an error message message. The function is not expected to return to the caller; if it does, the resulting behavior is undefined.

  Fatal errors are unrecoverable, and the only reasonable course of action is to abort the calling process. The default fatal error handler function writes a message to standard error and then calls `abort()`. One potential alternate implementation would be to call `exit()` with an exit status that indicates to the parent process (such as a watchdog process) that the current process has encountered an unrecoverable condition and should be respawned.

  In the current implementation, the only condition that will produce a fatal error is a memory allocation failure—that is, a `NULL` return value from `malloc()`, `calloc()`, or `realloc()`.

Function: void config_set_include_dir (config_t *config, const char *include_dir) ¶
Function: const char * config_get_include_dir (const config_t *config) ¶

  `config_set_include_dir()` specifies the include directory, include_dir, relative to which the files specified in ‘`@include`’ directives will be located for the configuration config. By default, there is no include directory, and all include files are expected to be relative to the current working directory. If include_dir is `NULL`, the default behavior is reinstated.

  For example, if the include directory is set to `/usr/local/etc`, the include directive ‘`@include "configs/extra.cfg"`’ would include the file `/usr/local/etc/configs/extra.cfg`.

  `config_get_include_dir()` returns the current include directory for the configuration config, or `NULL` if none is set.

Function: void config_set_include_func (config_include_fn_t func) ¶

  Since v1.7

  Specifies the include function func to use when processing include directives. If func is `NULL`, the default include function, `config_default_include_func()`, will be reinstated.

  The type config_include_fn_t is a type alias for a function whose signature is:

  Function: const char ** func (config_t *config, const char *include_dir, const char *path, const char **error) ¶

    The function receives the configuration config, the configuration’s current include directory include_dir, the argument to the include directive path; and a pointer at which to return an error message error.

    On success, the function should return a `NULL`-terminated array of paths. Any relative paths must be relative to the program’s current working directory. The contents of these files will be inlined at the point of inclusion, in the order that the paths appear in the array. Both the array and its elements should be heap allocated; the library will take ownership of and eventually free the strings in the array and the array itself.

    On failure, the function should return `NULL` and set *error to a static error string which should be used as the parse error for the configuration; the library does not take ownership of or free this string.

    The default include function, `config_default_include_func()`, simply returns a `NULL`-terminated array containing either a copy of path if it’s an absolute path, or a concatenation of include_dir and path if it’s a relative path.

  Application-supplied include functions can perform custom tasks like wildcard expansion or variable substitution. For example, consider the include directive:

      @include "configs/*.cfg"

  The include function would be invoked with the path ‘`configs/*.cfg`’ and could do wildcard expansion on that path, returning a list of paths to files with the file extension ‘`.cfg`’ in the subdirectory ‘`configs`’. Each of these files would then be inlined at the location of the include directive.

  Tasks like wildcard expansion and variable substitution are non-trivial to implement and typically require platform-specific code. In the interests of keeping the library as compact and platform-independent as possible, implementations of such include functions are not included.

Function: unsigned short config_get_float_precision (config_t *config) ¶
Function: void config_set_float_precision (config_t *config, unsigned short digits) ¶

  Since v1.6

  These functions get and set the number of decimal digits to output after the radix character when writing the configuration to a file or stream.

  Valid values for digits range from 0 (no decimals) to about 15 (implementation defined). This parameter has no effect on parsing.

  The default float precision is 6.

Function: int config_get_options (config_t *config) ¶
Function: void config_set_options (config_t *config, int options) ¶

  These functions get and set the options for the configuration config. The options affect how configurations are read and written. The following options are defined:

  `CONFIG_OPTION_AUTOCONVERT`

    Turning this option on enables number auto-conversion for the configuration. When this feature is enabled, an attempt to retrieve a floating point setting’s value into an integer (or vice versa), or store an integer to a floating point setting’s value (or vice versa) will cause the library to silently perform the necessary conversion (possibly leading to loss of data), rather than reporting failure. By default this option is turned off.

  `CONFIG_OPTION_SEMICOLON_SEPARATORS`

    This option controls whether a semicolon (‘;’) is output after each setting when the configuration is written to a file or stream. (The semicolon separators are optional in the configuration syntax.) By default this option is turned on.

  `CONFIG_OPTION_COLON_ASSIGNMENT_FOR_GROUPS`

    This option controls whether a colon (‘:’) is output between each group setting’s name and its value when the configuration is written to a file or stream. If the option is turned off, an equals sign (‘=’) is output instead. (These tokens are interchangeable in the configuration syntax.) By default this option is turned on.

  `CONFIG_OPTION_COLON_ASSIGNMENT_FOR_NON_GROUPS`

    This option controls whether a colon (‘:’) is output between each non-group setting’s name and its value when the configuration is written to a file or stream. If the option is turned off, an equals sign (‘=’) is output instead. (These tokens are interchangeable in the configuration syntax.) By default this option is turned off.

  `CONFIG_OPTION_OPEN_BRACE_ON_SEPARATE_LINE`

    This option controls whether an open brace (‘{’) will be written on its own line when the configuration is written to a file or stream. If the option is turned off, the brace will be written at the end of the previous line. By default this option is turned on.

  `CONFIG_OPTION_ALLOW_SCIENTIFIC_NOTATION`

    (Since v1.7) This option controls whether scientific notation may be used as appropriate when writing floating point values (corresponding to `printf()` ‘`%g`’ format) or should never be used (corresponding to `printf()` ‘`%f`’ format). By default this option is turned off.

  `CONFIG_OPTION_FSYNC`

    (Since v1.7.1) This option controls whether the `config_write_file()` function performs an fsync operation after writing the configuration and before closing the file. By default this option is turned off.

  `CONFIG_OPTION_ALLOW_OVERRIDES`

    (Since v1.7.3) This option controls whether duplicate settings override previous settings with the same name. If this option is turned off, duplicate settings are rejected. By default this option is turned off.

Function: int config_get_option (config_t *config, int option) ¶
Function: void config_set_option (config_t *config, int option, int flag) ¶

  Since v1.7

  These functions get and set the given option of the configuration config. The option is enabled if flag is `CONFIG_TRUE` and disabled if it is `CONFIG_FALSE`.

  See `config_set_options()` above for the list of available options.

Function: int config_get_auto_convert (const config_t *config) ¶
Function: void config_set_auto_convert (config_t *config, int flag) ¶

  These functions get and set the `CONFIG_OPTION_AUTOCONVERT` option. They are obsoleted by the `config_set_option()` and `config_get_option()` functions described above.

Function: unsigned short config_get_default_format (config_t * config) ¶
Function: void config_set_default_format (config_t * config, unsigned short format) ¶

  These functions, which are implemented as macros, get and set the default external format for settings in the configuration config. If a non-default format has not been set for a setting with `config_setting_set_format()`, this configuration-wide default format will be used instead when that setting is written to a file or stream.

Function: unsigned short config_get_tab_width (const config_t * config) ¶
Function: void config_set_tab_width (config_t * config, unsigned short width) ¶

  These functions, which are implemented as macros, get and set the tab width for the configuration config. The tab width affects the formatting of the configuration when it is written to a file or stream: each level of nesting is indented by width spaces, or by a single tab character if width is 0. The tab width has no effect on parsing.

  Valid tab widths range from 0 to 15. The default tab width is 2.

Function: int config_lookup_int (const config_t * config, const char * path, int * value) ¶
Function: int config_lookup_int64 (const config_t * config, const char * path, long long * value) ¶
Function: int config_lookup_float (const config_t * config, const char * path, double * value) ¶
Function: int config_lookup_bool (const config_t * config, const char * path, int * value) ¶
Function: int config_lookup_string (const config_t * config, const char * path, const char ** value) ¶

  These functions look up the value of the setting in the configuration config specified by the path path. They store the value of the setting at value and return `CONFIG_TRUE` on success. If the setting was not found or if the type of the value did not match the type requested, they leave the data pointed to by value unmodified and return `CONFIG_FALSE`.

  Storage for the string returned by `config_lookup_string()` is managed by the library and released automatically when the setting is destroyed or when the setting’s value is changed; the string must not be freed by the caller.

Function: config_setting_t * config_lookup (const config_t * config, const char * path) ¶

  This function locates the setting in the configuration config specified by the path path. It returns a pointer to the `config_setting_t` structure on success, or `NULL` if the setting was not found.

Function: const config_setting_t * config_lookup_const (const config_t * config, const char * path) ¶

  Since v1.7.4

  This function is identical to `config_lookup()`, except that the setting is returned as a `const` structure.

Function: config_setting_t * config_setting_lookup (const config_setting_t * setting, const char * path) ¶

  This function locates a setting by a path path relative to the setting setting. It returns a pointer to the `config_setting_t` structure on success, or `NULL` if the setting was not found.

Function: const config_setting_t * config_setting_lookup_const (const config_setting_t * setting, const char * path) ¶

  Since v1.7.4

  This function is identical to `config_setting_lookup()`, except that the setting is returned as a `const` structure.

Function: int config_setting_get_int (const config_setting_t * setting) ¶
Function: long long config_setting_get_int64 (const config_setting_t * setting) ¶
Function: double config_setting_get_float (const config_setting_t * setting) ¶
Function: int config_setting_get_bool (const config_setting_t * setting) ¶
Function: const char * config_setting_get_string (const config_setting_t * setting) ¶

  These functions return the value of the given setting. If the type of the setting does not match the type requested, a 0 or `NULL` value is returned. Storage for the string returned by `config_setting_get_string()` is managed by the library and released automatically when the setting is destroyed or when the setting’s value is changed; the string must not be freed by the caller.

Function: int config_setting_get_int_safe (const config_setting_t * setting, int *value) ¶
Function: int config_setting_get_int64_safe (const config_setting_t * setting, long long *value) ¶
Function: int config_setting_get_float_safe (const config_setting_t * setting, double *value) ¶
Function: int config_setting_get_bool_safe (const config_setting_t * setting, int *value) ¶
Function: int config_setting_get_string_safe (const config_setting_t * setting, const char **value) ¶

  Since v1.8.1

  These functions are “safe” versions of the corresponding functions whose names do not have the `_safe` suffix, in that they do not silently return a default value if the setting is not of the expected type. Specifically, if setting is of the expected type (or its value can be converted to the expected type, if auto-conversion is enabled), they store its value at value and return `CONFIG_TRUE`; otherwise, they return `CONFIG_FALSE`.

Function: int config_setting_set_int (config_setting_t * setting, int value) ¶
Function: int config_setting_set_int64 (config_setting_t * setting, long long value) ¶
Function: int config_setting_set_float (config_setting_t * setting, double value) ¶
Function: int config_setting_set_bool (config_setting_t * setting, int value) ¶
Function: int config_setting_set_string (config_setting_t * setting, const char *value) ¶

  These functions set the value of the given setting to value. On success, they return `CONFIG_TRUE`. If the setting does not match the type of the value, they return `CONFIG_FALSE`. `config_setting_set_string()` makes a copy of the passed string value, so it may be subsequently freed or modified by the caller without affecting the value of the setting.

Function: int config_setting_lookup_int (const config_setting_t * setting, const char * name, int * value) ¶
Function: int config_setting_lookup_int64 (const config_setting_t * setting, const char * name, long long * value) ¶
Function: int config_setting_lookup_float (const config_setting_t * setting, const char * name, double * value) ¶
Function: int config_setting_lookup_bool (const config_setting_t * setting, const char * name, int * value) ¶
Function: int config_setting_lookup_string (const config_setting_t * setting, const char * name, const char ** value) ¶

  These functions look up the value of the child setting named name of the setting setting. They store the value at value and return `CONFIG_TRUE` on success. If the setting was not found or if the type of the value did not match the type requested, they leave the data pointed to by value unmodified and return `CONFIG_FALSE`.

  Storage for the string returned by `config_setting_lookup_string()` is managed by the library and released automatically when the setting is destroyed or when the setting’s value is changed; the string must not be freed by the caller.

Function: unsigned short config_setting_get_format (config_setting_t * setting) ¶
Function: int config_setting_set_format (config_setting_t * setting, unsigned short format) ¶

  These functions get and set the external format for the setting setting.

  The format must be one of the constants `CONFIG_FORMAT_DEFAULT`, `CONFIG_FORMAT_BIN` (since version 1.8), `CONFIG_FORMAT_OCT` (since version 1.8.1), or `CONFIG_FORMAT_HEX`. All settings support the `CONFIG_FORMAT_DEFAULT` format. The remaining formats specify base-2, base-8, and base-16 representations, respectively, for integer values, and hence only apply to settings of type `CONFIG_TYPE_INT` and `CONFIG_TYPE_INT64`. If format is invalid for the given setting, it is ignored.

  If a non-default format has not been set for the setting, `config_setting_get_format()` returns the default format for the configuration, as set by `config_set_default_format()`.

  `config_setting_set_format()` returns `CONFIG_TRUE` on success and `CONFIG_FALSE` on failure.

Function: config_setting_t * config_setting_get_member (config_setting_t * setting, const char * name) ¶

  This function fetches the child setting named name from the group setting. It returns the requested setting on success, or `NULL` if the setting was not found or if setting is not a group.

Function: config_setting_t * config_setting_get_elem (const config_setting_t * setting, unsigned int index) ¶

  This function fetches the element at the given index index in the setting setting, which must be an array, list, or group. It returns the requested setting on success, or `NULL` if index is out of range or if setting is not an array, list, or group.

Function: int config_setting_get_int_elem (const config_setting_t * setting, int index) ¶
Function: long long config_setting_get_int64_elem (const config_setting_t * setting, int index) ¶
Function: double config_setting_get_float_elem (const config_setting_t * setting, int index) ¶
Function: int config_setting_get_bool_elem (const config_setting_t * setting, int index) ¶
Function: const char * config_setting_get_string_elem (const config_setting_t * setting, int index) ¶

  These functions return the value at the specified index index in the setting setting. If the setting is not an array or list, or if the type of the element does not match the type requested, or if index is out of range, they return 0 or `NULL`. Storage for the string returned by `config_setting_get_string_elem()` is managed by the library and released automatically when the setting is destroyed or when its value is changed; the string must not be freed by the caller.

Function: config_setting_t * config_setting_set_int_elem (config_setting_t * setting, int index, int value) ¶
Function: config_setting_t * config_setting_set_int64_elem (config_setting_t * setting, int index, long long value) ¶
Function: config_setting_t * config_setting_set_float_elem (config_setting_t * setting, int index, double value) ¶
Function: config_setting_t * config_setting_set_bool_elem (config_setting_t * setting, int index, int value) ¶
Function: config_setting_t * config_setting_set_string_elem (config_setting_t * setting, int index, const char * value) ¶

  These functions set the value at the specified index index in the setting setting to value. If index is negative, a new element is added to the end of the array or list. On success, these functions return a pointer to the setting representing the element. If the setting is not an array or list, or if the setting is an array and the type of the array does not match the type of the value, or if index is out of range, they return `NULL`. `config_setting_set_string_elem()` makes a copy of the passed string value, so it may be subsequently freed or modified by the caller without affecting the value of the setting.

Function: config_setting_t * config_setting_add (config_setting_t * parent, const char * name, int type) ¶

  This function adds a new child setting or element to the setting parent, which must be a group, array, or list. If parent is an array or list, the name parameter is ignored and may be `NULL`.

  The function returns the new setting on success, or `NULL` if parent is not a group, array, or list; or if there is already a child setting of parent named name; or if type is invalid. If type is a scalar type, the new setting will have a default value of 0, 0.0, `false`, or `NULL`, as appropriate.

Function: int config_setting_remove (config_setting_t * parent, const char * name) ¶

  This function removes and destroys the setting named name from the parent setting parent, which must be a group. Any child settings of the setting are recursively destroyed as well.

  The name parameter can also specify a setting path relative to the provided parent. (In that case, the setting will be looked up and removed.)

  The function returns `CONFIG_TRUE` on success. If parent is not a group, or if it has no setting with the given name, it returns `CONFIG_FALSE`.

Function: int config_setting_remove_elem (config_setting_t * parent, unsigned int index) ¶

  This function removes the child setting at the given index index from the setting parent, which must be a group, list, or array. Any child settings of the removed setting are recursively destroyed as well.

  The function returns `CONFIG_TRUE` on success. If parent is not a group, list, or array, or if index is out of range, it returns `CONFIG_FALSE`.

Function: config_setting_t * config_root_setting (const config_t * config) ¶

  This function, which is implemented as a macro, returns the root setting for the configuration config. The root setting is a group.

Function: const char * config_setting_name (const config_setting_t * setting) ¶

  This function returns the name of the given setting, or `NULL` if the setting has no name. Storage for the returned string is managed by the library and released automatically when the setting is destroyed; the string must not be freed by the caller.

Function: config_setting_t * config_setting_parent (const config_setting_t * setting) ¶

  This function returns the parent setting of the given setting, or `NULL` if setting is the root setting.

Function: int config_setting_is_root (const config_setting_t * setting) ¶

  This function returns `CONFIG_TRUE` if the given setting is the root setting, and `CONFIG_FALSE` otherwise.

Function: int config_setting_index (const config_setting_t * setting) ¶

  This function returns the index of the given setting within its parent setting. If setting is the root setting, this function returns -1.

Function: int config_setting_length (const config_setting_t * setting) ¶

  This function returns the number of settings in a group, or the number of elements in a list or array. For other types of settings, it returns 0.

Function: int config_setting_type (const config_setting_t * setting) ¶

  This function returns the type of the given setting. The return value is one of the constants `CONFIG_TYPE_INT`, `CONFIG_TYPE_INT64`, `CONFIG_TYPE_FLOAT`, `CONFIG_TYPE_STRING`, `CONFIG_TYPE_BOOL`, `CONFIG_TYPE_ARRAY`, `CONFIG_TYPE_LIST`, or `CONFIG_TYPE_GROUP`.

Function: int config_setting_is_group (const config_setting_t * setting) ¶
Function: int config_setting_is_array (const config_setting_t * setting) ¶
Function: int config_setting_is_list (const config_setting_t * setting) ¶

  These convenience functions, which are implemented as macros, test if the setting setting is of a given type. They return `CONFIG_TRUE` or `CONFIG_FALSE`.

Function: int config_setting_is_aggregate (const config_setting_t * setting) ¶
Function: int config_setting_is_scalar (const config_setting_t * setting) ¶
Function: int config_setting_is_number (const config_setting_t * setting) ¶

  These convenience functions, some of which are implemented as macros, test if the setting setting is of an aggregate type (a group, array, or list), of a scalar type (integer, 64-bit integer, floating point, boolean, or string), and of a number (integer, 64-bit integer, or floating point), respectively. They return `CONFIG_TRUE` or `CONFIG_FALSE`.

Function: const char * config_setting_source_file (const config_setting_t * setting) ¶

  This function returns the name of the file from which the setting setting was read, or NULL if the setting was not read from a file. This information is useful for reporting application-level errors. Storage for the returned string is managed by the library and released automatically when the configuration is destroyed; the string must not be freed by the caller.

Function: unsigned int config_setting_source_line (const config_setting_t * setting) ¶

  This function returns the line number of the configuration file or stream at which the setting setting was read, or 0 if no line number is available. This information is useful for reporting application-level errors.

Function: void config_set_hook (config_t * config, void * hook) ¶
Function: void * config_get_hook (const config_t * config) ¶

  Since v1.7

  These functions make it possible to attach arbitrary data to a configuration structure, for instance a “wrapper” or “peer” object written in another programming language.

Function: void config_setting_set_hook (config_setting_t * setting, void * hook) ¶
Function: void * config_setting_get_hook (const config_setting_t * setting) ¶

  These functions make it possible to attach arbitrary data to each setting structure, for instance a “wrapper” or “peer” object written in another programming language. The destructor function, if one has been supplied via a call to `config_set_destructor()`, will be called by the library to dispose of this data when the setting itself is destroyed. There is no default destructor.

Function: void config_set_destructor (config_t * config, void (* destructor)(void *)) ¶

  This function assigns the destructor function destructor for the configuration config. This function accepts a single `void *` argument and has no return value. See `config_setting_set_hook()` above for more information.

Next: Example Programs, Previous: The C API, Up: libconfig [Contents][Index]

## 4 The C++ API

This chapter describes the C++ library API. The class `Config` represents a configuration, and the class `Setting` represents a configuration setting. Note that by design, neither of these classes provides a public copy constructor or assignment operator. Therefore, instances of these classes may only be passed between functions via references or pointers.

The library defines a group of exceptions, all of which extend the common base exception `ConfigException`.

A `SettingTypeException` is thrown when the type of a setting’s value does not match the type requested.

Method on SettingTypeException: SettingTypeException (const Setting &setting) ¶
Method on SettingTypeException: SettingTypeException (const Setting &setting, int index) ¶
Method on SettingTypeException: SettingTypeException (const Setting &setting, const char *name) ¶

  These methods construct `SettingTypeException` objects for the given setting and/or member index or name.

A `SettingRangeException` is thrown when an attempt is made to read a 64-bit integer configuration setting into an integer variable, and the value of that setting is outside the range of an integer.

Method on SettingRangeException: SettingRangeException (const Setting &setting) ¶
Method on SettingRangeException: SettingRangeException (const Setting &setting, int index) ¶
Method on SettingRangeException: SettingRangeException (const Setting &setting, const char *name) ¶

  Since v1.7.4

  These methods construct `SettingRangeException` objects for the given setting and/or member index or name.

A `SettingNotFoundException` is thrown when a setting is not found.

Method on SettingNotFoundException: SettingNotFoundException (const Setting &setting, int index) ¶
Method on SettingNotFoundException: SettingNotFoundException (const Setting &setting, const char *name) ¶
Method on SettingNotFoundException: SettingNotFoundException (const char *path) ¶

  These methods construct `SettingTypeException` objects for the given setting and member index or name, or path path.

A `SettingNameException` is thrown when an attempt is made to add a new setting with a non-unique or invalid name.

Method on SettingNameException: SettingNameException (const Setting &setting, const char *name) ¶

  This method constructs a `SettingNameExcpetion` object for the given setting and member name name.

A `ParseException` is thrown when a parse error occurs while reading a configuration from a stream.

Method on ParseException: ParseException (const char *file, int line, const char *error) ¶

  This method constructs a `ParseException` object with the given filename file, line number line, and error message error.

A `FileIOException` is thrown when an I/O error occurs while reading/writing a configuration from/to a file.

`SettingTypeException`, `SettingNotFoundException`, and `SettingNameException` all extend the common base exception `SettingException`, which provides the following method:

Method on SettingException: const char * getPath () const ¶

  This method returns the path to the setting associated with the exception, or `NULL` if there is no applicable path.

The remainder of this chapter describes the methods for manipulating configurations and configuration settings.

Method on Config: Config () ¶
Method on Config: ~Config () ¶

  These methods create and destroy `Config` objects.

Method on Config: void clear () ¶

  Since v1.7

  This method clears the configuration. All child settings of the root setting are recursively destroyed. All other attributes of the configuration are left unchanged.

Method on Config: void read (FILE * stream) ¶
Method on Config: void write (FILE * stream) const ¶

  The `read()` method reads and parses a configuration from the given stream. A `ParseException` is thrown if a parse error occurs.

  The `write()` method writes the configuration to the given stream.

Method on Config: void readFile (const char * filename) ¶
Method on Config: void readFile (const std::string &filename) ¶

  The `readFile()` method reads and parses a configuration from the file named filename. A `ParseException` is thrown if a parse error occurs. A `FileIOException` is thrown if the file cannot be read.

Method on Config: void writeFile (const char * filename) ¶
Method on Config: void writeFile (const std::string &filename) ¶

  The `writeFile()` method writes the configuration to the file named filename. A `FileIOException` is thrown if the file cannot be written.

Method on Config: void readString (const char * str) ¶
Method on Config: void readString (const std::string &str) ¶

  These methods read and parse a configuration from the string str. A `ParseException` is thrown if a parse error occurs.

Method on ParseException: const char * getError () const ¶
Method on ParseException: const char * getFile () const ¶
Method on ParseException: int getLine () const ¶

  If a call to `readFile()`, `readString()`, or `read()` resulted in a `ParseException`, these methods can be called on the exception object to obtain the text, filename, and line number of the parse error. Storage for the strings returned by `getError()` and `getFile()` are managed by the library; the strings must not be freed by the caller.

Method on Config: void setIncludeDir (const char *includeDir) ¶
Method on Config: const char * getIncludeDir () const ¶

  The `setIncludeDir()` method specifies the include directory, includeDir, relative to which the files specified in ‘`@include`’ directives will be located for the configuration. By default, there is no include directory, and all include files are expected to be relative to the current working directory. If includeDir is `NULL`, the default behavior is reinstated.

  For example, if the include directory is set to `/usr/local/etc`, the include directive ‘`@include "configs/extra.cfg"`’ would include the file `/usr/local/etc/configs/extra.cfg`.

  `getIncludeDir()` returns the current include directory for the configuration, or `NULL` if none is set.

Method on Config: virtual const char ** evaluateIncludePath (const char * path, const char ** error) ¶

  Since v1.7

  This method is called to evaluate the path of an `@include` directive. The path is the literal path argument of the directive. The method may be overridden in a subclass to perform tasks like wildcard expansion and variable substitution.

  On success, the method should return a `NULL`-terminated array of paths. Any relative paths must be relative to the program’s current working directory. The contents of these files will be inlined at the point of inclusion, in the order that the paths appear in the array. Both the array and its elements should be heap allocated; the library will take ownership of and eventually free the strings in the array and the array itself.

  On failure, the function should return `NULL` and set *error to a static error string which should be used as the parse error for the configuration; the library does not take ownership of or free this string.

  The default implementation simply returns a `NULL`-terminated array containing either a copy of path if it’s an absolute path, or a concatenation of the include directory and path if it’s a relative path.

  For more information see `config_set_include_func()` in the C API.

Method on Config: int getOptions () const ¶
Method on Config: void setOptions (int options) ¶

  These methods get and set the options for the configuration. The options affect how configurations are read and written. The parameter options should be a bitwise-OR of the following Config::Option enumeration values:

  `Config::OptionAutoConvert`

    Turning this option on enables number auto-conversion for the configuration. When this feature is enabled, an attempt to retrieve a floating point setting’s value into an integer (or vice versa), or store an integer to a floating point setting’s value (or vice versa) will cause the library to silently perform the necessary conversion (possibly leading to loss of data), rather than reporting failure. By default this option is turned off.

  `Config::OptionSemicolonSeparators`

    This option controls whether a semicolon (‘;’) is output after each setting when the configuration is written to a file or stream. (The semicolon separators are optional in the configuration syntax.) By default this option is turned on.

  `Config::OptionColonAssignmentForGroups`

    This option controls whether a colon (‘:’) is output between each group setting’s name and its value when the configuration is written to a file or stream. If the option is turned off, an equals sign (‘=’) is output instead. (These tokens are interchangeable in the configuration syntax.) By default this option is turned on.

  `Config::OptionColonAssignmentForNonGroups`

    This option controls whether a colon (‘:’) is output between each non-group setting’s name and its value when the configuration is written to a file or stream. If the option is turned off, an equals sign (‘=’) is output instead. (These tokens are interchangeable in the configuration syntax.) By default this option is turned off.

  `Config::OptionOpenBraceOnSeparateLine`

    This option controls whether an open brace (‘{’) will be written on its own line when the configuration is written to a file or stream. If the option is turned off, the brace will be written at the end of the previous line. By default this option is turned on.

  `Config::OptionAllowScientificNotation`

    (Since v1.7) This option controls whether scientific notation may be used as appropriate when writing floating point values (corresponding to `printf()` ‘`%g`’ format) or should never be used (corresponding to `printf()` ‘`%f`’ format). By default this option is turned off.

  `Config::OptionFsync`

    (Since v1.7.1) This option controls whether the `writeFile()` method performs an fsync operation after writing the configuration and before closing the file. By default this option is turned off.

  `Config::OptionAllowOverrides`

    (Since v1.7.3) This option controls whether duplicate settings override previous settings with the same name. If this option is turned off, duplicate settings are rejected. By default this option is turned off.

Method on Config: bool getOption (Config::Option option) const ¶
Method on Config: void setOption (Config::Option option, bool flag) ¶

  Since v1.7

  These methods get and set the option option for the configuration. The option is enabled if flag is `true` and disabled if it is `false`.

  See `setOptions()` above for the list of available options.

Method on Config: bool getAutoConvert () const ¶
Method on Config: void setAutoConvert (bool flag) ¶

  These methods get and set the `OptionAutoConvert` option. They are obsoleted by the `setOption()` and `getOption()` methods described above.

Method on Config: Setting::Format getDefaultFormat () const ¶
Method on Config: void setDefaultFormat (Setting::Format format) ¶

  These methods get and set the default external format for settings in the configuration. If a non-default format has not been set for a setting with `Setting::setFormat()`, this configuration-wide default format will be used instead when that setting is written to a file or stream.

Method on Config: unsigned short getTabWidth () const ¶
Method on Config: void setTabWidth (unsigned short width) ¶

  These methods get and set the tab width for the configuration. The tab width affects the formatting of the configuration when it is written to a file or stream: each level of nesting is indented by width spaces, or by a single tab character if width is 0. The tab width has no effect on parsing.

  Valid tab widths range from 0 to 15. The default tab width is 2.

Method on Config: unsigned short getFloatPrecision () const ¶
Method on Config: void setFloatPrecision (unsigned short width) ¶

  These methods get and set the float precision for the configuration. This parameter influences the formatting of floating point settings in the configuration when it is written to a file or stream. Float precision has no effect on parsing.

  Valid precisions range from 0 to about 15 (implementation dependent), though the library will accept and store values up to 255.

Method on Config: Setting & getRoot () const ¶

  This method returns the root setting for the configuration, which is a group.

Method on Config: Setting & lookup (const std::string &path) const ¶
Method on Config: Setting & lookup (const char * path) const ¶

  These methods locate the setting specified by the path path. If the requested setting is not found, a `SettingNotFoundException` is thrown.

Method on Config: bool exists (const std::string &path) const ¶
Method on Config: bool exists (const char *path) const ¶

  These methods test if a setting with the given path exists in the configuration. They return `true` if the setting exists, and `false` otherwise. These methods do not throw exceptions.

Method on Config: bool lookupValue (const char *path, bool &value) const ¶
Method on Config: bool lookupValue (const std::string &path, bool &value) const ¶
Method on Config: bool lookupValue (const char *path, int &value) const ¶
Method on Config: bool lookupValue (const std::string &path, int &value) const ¶
Method on Config: bool lookupValue (const char *path, unsigned int &value) const ¶
Method on Config: bool lookupValue (const std::string &path, unsigned int &value) const ¶
Method on Config: bool lookupValue (const char *path, long long &value) const ¶
Method on Config: bool lookupValue (const std::string &path, long long &value) const ¶
Method on Config: bool lookupValue (const char *path, float &value) const ¶
Method on Config: bool lookupValue (const std::string &path, float &value) const ¶
Method on Config: bool lookupValue (const char *path, double &value) const ¶
Method on Config: bool lookupValue (const std::string &path, double &value) const ¶
Method on Config: bool lookupValue (const char *path, const char *&value) const ¶
Method on Config: bool lookupValue (const std::string &path, const char *&value) const ¶
Method on Config: bool lookupValue (const char *path, std::string &value) const ¶
Method on Config: bool lookupValue (const std::string &path, std::string &value) const ¶

  These are convenience methods for looking up the value of a setting with the given path. If the setting is found and is of an appropriate type, the value is stored in value and the method returns `true`. Otherwise, value is left unmodified and the method returns `false`. These methods do not throw exceptions.

  Storage for const char * values is managed by the library and released automatically when the setting is destroyed or when its value is changed; the string must not be freed by the caller. For safety and convenience, always assigning string values to a `std::string` is suggested.

  Since these methods have boolean return values and do not throw exceptions, they can be used within boolean logic expressions. The following example presents a concise way to look up three values at once and perform error handling if any of them are not found or are of the wrong type:

      int var1;
      double var2;
      const char *var3;

      if(config.lookupValue("values.var1", var1)
         && config.lookupValue("values.var2", var2)
         && config.lookupValue("values.var3", var3))
      {
        // use var1, var2, var3
      }
      else
      {
        // error handling here
      }

  This approach also takes advantage of the short-circuit evaluation rules of C++, e.g., if the first lookup fails (returning `false`), the remaining lookups are skipped entirely.

Method on Setting: operator bool () const ¶
Method on Setting: operator int () const ¶
Method on Setting: operator unsigned int () const ¶
Method on Setting: operator long () const ¶
Method on Setting: operator unsigned long () const ¶
Method on Setting: operator long long () const ¶
Method on Setting: operator unsigned long long () const ¶
Method on Setting: operator float () const ¶
Method on Setting: operator double () const ¶
Method on Setting: operator const char * () const ¶
Method on Setting: operator std::string () const ¶
Method on Setting: const char * c_str () const ¶

  These cast operators allow a `Setting` object to be assigned to a variable of type bool if it is of type `TypeBoolean`; int, unsigned int; `long long` or `unsigned long long` if it is of type `TypeInt64`, float or double if it is of type `TypeFloat`; or const char * or std::string if it is of type `TypeString`.

  Values of type `TypeInt` or `TypeInt64` may be assigned to variables of type long, or unsigned long, depending on the sizes of those types on the host system.

  Storage for const char * return values is managed by the library and released automatically when the setting is destroyed or when its value is changed; the string must not be freed by the caller. For safety and convenience, always assigning string return values to a `std::string` is suggested.

  The following examples demonstrate this usage:

      long width = config.lookup("application.window.size.w");

      bool splashScreen = config.lookup("application.splash_screen");

      std::string title = config.lookup("application.window.title");

  Note that certain conversions can lead to loss of precision or clipping of values, e.g., assigning a negative value to an unsigned int (in which case the value will be treated as 0), or a double-precision value to a float. The library does not treat these lossy conversions as errors.

  Perhaps surprisingly, the following code in particular will cause a compiler error:

      std::string title;
      .
      .
      .
      title = config.lookup("application.window.title");

  This is because the assignment operator of `std::string` is being invoked with a `Setting &` as an argument. The compiler is unable to make an implicit conversion because both the `const char *` and the `std::string` cast operators of `Setting` are equally appropriate. This is not a bug in libconfig; providing only the `const char *` cast operator would resolve this particular ambiguity, but would cause assignments to `std::string` like the one in the previous example to produce a compiler error. (To understand why, see section 11.4.1 of The C++ Programming Language.)

  The solution to this problem is to use an explicit conversion that avoids the construction of an intermediate `std::string` object, as follows:

      std::string title;
      .
      .
      .
      title = (const char *)config.lookup("application.window.title");

  Or, alternatively, use the `c_str()` method, which has the same effect:

      std::string title;
      .
      .
      .
      title = config.lookup("application.window.title").c_str();

  A `SettingRangeException` is thrown under the following circumstances:

  - The setting’s value is a 64-bit integer, and is being cast to a smaller integer type such as `int` or `unsigned long`, but the value is outside the range of that type.
  - The setting’s value is a negative integer, and is being cast to an unsigned integer type such as `unsigned int`.

  If the assignment is invalid due to a type mismatch, a `SettingTypeException` is thrown.

Method on Setting: Setting & operator= (bool value) ¶
Method on Setting: Setting & operator= (int value) ¶
Method on Setting: Setting & operator= (long value) ¶
Method on Setting: Setting & operator= (const long long &value) ¶
Method on Setting: Setting & operator= (float value) ¶
Method on Setting: Setting & operator= (const double &value) ¶
Method on Setting: Setting & operator= (const char *value) ¶
Method on Setting: Setting & operator= (const std::string &value) ¶

  These assignment operators allow values of type bool, int, long, long long, float, double, const char *, and std::string to be assigned to a setting. In the case of strings, the library makes a copy of the passed string value, so it may be subsequently freed or modified by the caller without affecting the value of the setting.

  The following example code looks up a (presumably) integer setting and changes its value:

      Setting &setting = config.lookup("application.window.size.w");
      setting = 1024;

  If the assignment is invalid due to a type mismatch, a `SettingTypeException` is thrown.

Method on Setting: Setting & operator[] (int index) const ¶
Method on Setting: Setting & operator[] (const std::string &name) const ¶
Method on Setting: Setting & operator[] (const char *name) const ¶

  A `Setting` object may be subscripted with an integer index index if it is an array or list, or with either a string name or an integer index index if it is a group. For example, the following code would produce the string ‘`Last Name`’ when applied to the example configuration in Configuration Files.

      Setting& setting = config.lookup("application.misc");
      const char *s = setting["columns"][0];

  If the setting is not an array, list, or group, a `SettingTypeException` is thrown. If the subscript (index or name) does not refer to a valid element, a `SettingNotFoundException` is thrown.

  Iterating over a group’s child settings with an integer index will return the settings in the same order that they appear in the configuration.

Method on Setting: Setting & lookup (const char * path) const ¶
Method on Setting: Setting & lookup (const std::string &path) const ¶

  These methods locate a setting by a path path relative to this setting. If requested setting is not found, a `SettingNotFoundException` is thrown.

Method on Setting: bool lookupValue (const char *name, bool &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, bool &value) const ¶
Method on Setting: bool lookupValue (const char *name, int &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, int &value) const ¶
Method on Setting: bool lookupValue (const char *name, unsigned int &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, unsigned int &value) const ¶
Method on Setting: bool lookupValue (const char *name, long long &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, long long &value) const ¶
Method on Setting: bool lookupValue (const char *name, unsigned long long &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, unsigned long long &value) const ¶
Method on Setting: bool lookupValue (const char *name, float &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, float &value) const ¶
Method on Setting: bool lookupValue (const char *name, double &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, double &value) const ¶
Method on Setting: bool lookupValue (const char *name, const char *&value) const ¶
Method on Setting: bool lookupValue (const std::string &name, const char *&value) const ¶
Method on Setting: bool lookupValue (const char *name, std::string &value) const ¶
Method on Setting: bool lookupValue (const std::string &name, std::string &value) const ¶

  These are convenience methods for looking up the value of a child setting with the given name. If the setting is found and is of an appropriate type, the value is stored in value and the method returns `true`. Otherwise, value is left unmodified and the method returns `false`. These methods do not throw exceptions.

  Storage for const char * values is managed by the library and released automatically when the setting is destroyed or when its value is changed; the string must not be freed by the caller. For safety and convenience, always assigning string values to a `std::string` is suggested.

  Since these methods have boolean return values and do not throw exceptions, they can be used within boolean logic expressions. The following example presents a concise way to look up three values at once and perform error handling if any of them are not found or are of the wrong type:

      int var1;
      double var2;
      const char *var3;

      if(setting.lookupValue("var1", var1)
         && setting.lookupValue("var2", var2)
         && setting.lookupValue("var3", var3))
      {
        // use var1, var2, var3
      }
      else
      {
        // error handling here
      }

  This approach also takes advantage of the short-circuit evaluation rules of C++, e.g., if the first lookup fails (returning `false`), the remaining lookups are skipped entirely.

Method on Setting: Setting & add (const std::string &name, Setting::Type type) ¶
Method on Setting: Setting & add (const char *name, Setting::Type type) ¶

  These methods add a new child setting with the given name and type to the setting, which must be a group. They return a reference to the new setting. If the setting already has a child setting with the given name, or if the name is invalid, a `SettingNameException` is thrown. If the setting is not a group, a `SettingTypeException` is thrown.

  Once a setting has been created, neither its name nor type can be changed.

Method on Setting: Setting & add (Setting::Type type) ¶

  This method adds a new element to the setting, which must be of type `TypeArray` or `TypeList`. If the setting is an array which currently has zero elements, the type parameter (which must be `TypeInt`, `TypeInt64`, `TypeFloat`, `TypeBool`, or `TypeString`) determines the type for the array; otherwise it must match the type of the existing elements in the array.

  The method returns the new setting on success. If type is a scalar type, the new setting will have a default value of 0, 0.0, `false`, or `NULL`, as appropriate.

  The method throws a `SettingTypeException` if the setting is not an array or list, or if type is invalid.

Method on Setting: void remove (const std::string &name) ¶
Method on Setting: void remove (const char *name) ¶

  These methods remove the child setting with the given name from the setting, which must be a group. Any child settings of the removed setting are recursively destroyed as well.

  If the setting is not a group, a `SettingTypeException` is thrown. If the setting does not have a child setting with the given name, a `SettingNotFoundException` is thrown.

Method on Setting: void remove (unsigned int index) ¶

  This method removes the child setting at the given index index from the setting, which must be a group, list, or array. Any child settings of the removed setting are recursively destroyed as well.

  If the setting is not a group, list, or array, a `SettingTypeException` is thrown. If index is out of range, a `SettingNotFoundException` is thrown.

Method on Setting: const char * getName () const ¶

  This method returns the name of the setting, or `NULL` if the setting has no name. Storage for the returned string is managed by the library and released automatically when the setting is destroyed; the string must not be freed by the caller. For safety and convenience, consider assigning the return value to a `std::string`.

Method on Setting: std::string getPath () const ¶

  This method returns the complete dot-separated path to the setting. Settings which do not have a name (list and array elements) are represented by their index in square brackets.

Method on Setting: Setting & getParent () const ¶

  This method returns the parent setting of the setting. If the setting is the root setting, a `SettingNotFoundException` is thrown.

Method on Setting: bool isRoot () const ¶

  This method returns `true` if the setting is the root setting, and `false` otherwise.

Method on Setting: int getIndex () const ¶

  This method returns the index of the setting within its parent setting. When applied to the root setting, this method returns -1.

Method on Setting: Setting::Type getType () const ¶

  This method returns the type of the setting. The `Setting::Type` enumeration consists of the following constants: `TypeInt`, `TypeInt64`, `TypeFloat`, `TypeString`, `TypeBoolean`, `TypeArray`, `TypeList`, and `TypeGroup`.

Method on Setting: Setting::Format getFormat () const ¶
Method on Setting: void setFormat (Setting::Format format) ¶

  These methods get and set the external format for the setting.

  The Setting::Format enumeration consists of the following constants: `FormatDefault`, `FormatBin` (since version 1.8), `FormatOct` (since version 1.8.1), and `FormatHex`. All settings support the `FormatDefault` format. The remaining formats specify base-2, base-8, and base-16 representations, respectively, for integer values; hence these only apply to settings of type `TypeInt` and `TypeInt64`. If format is invalid for the given setting, it is ignored.

Method on Setting: bool exists (const std::string &name) const ¶
Method on Setting: bool exists (const char *name) const ¶

  These methods test if the setting has a child setting with the given name. They return `true` if the setting exists, and `false` otherwise. These methods do not throw exceptions.

Method on Setting: iterator begin () ¶
Method on Setting: iterator end () ¶
Method on Setting: const_iterator begin () ¶
Method on Setting: const_iterator end () ¶

  These methods return STL-style iterators that can be used to enumerate the child settings of a given setting. If the setting is not an array, list, or group, they throw a `SettingTypeException`.

Method on Setting: int getLength () const ¶

  This method returns the number of settings in a group, or the number of elements in a list or array. For other types of settings, it returns 0.

Method on Setting: bool isGroup () const ¶
Method on Setting: bool isArray () const ¶
Method on Setting: bool isList () const ¶

  These convenience methods test if a setting is of a given type.

Method on Setting: bool isAggregate () const ¶
Method on Setting: bool isScalar () const ¶
Method on Setting: bool isNumber () const ¶
Method on Setting: bool isString () const ¶

  These convenience methods test if a setting is of an aggregate type (a group, array, or list), of a scalar type (integer, 64-bit integer, floating point, boolean, or string), of a number (integer, 64-bit integer, or floating point), and of a string respectively.

Method on Setting: const char * getSourceFile () const ¶

  This method returns the name of the file from which the setting was read, or NULL if the setting was not read from a file. This information is useful for reporting application-level errors. Storage for the returned string is managed by the library and released automatically when the configuration is destroyed; the string must not be freed by the caller.

Method on Setting: unsigned int getSourceLine () const ¶

  This method returns the line number of the configuration file or stream at which the setting setting was read, or 0 if no line number is available. This information is useful for reporting application-level errors.

Next: Other Bindings and Implementations, Previous: The C++ API, Up: libconfig [Contents][Index]

## 5 Example Programs

Practical example programs that illustrate how to use libconfig from both C and C++ are included in the `examples` subdirectory of the distribution. These examples include:

`examples/c/example1.c`

  An example C program that reads a configuration from an existing file `example.cfg` (also located in `examples/c`) and displays some of its contents.

`examples/c++/example1.cpp`

  The C++ equivalent of `example1.c`.

`examples/c/example2.c`

  An example C program that reads a configuration from an existing file `example.cfg` (also located in `examples/c`), adds new settings to the configuration, and writes the updated configuration to another file.

`examples/c++/example2.cpp`

  The C++ equivalent of `example2.c`

`examples/c/example3.c`

  An example C program that constructs a new configuration in memory and writes it to a file.

`examples/c++/example3.cpp`

  The C++ equivalent of `example3.c`

`examples/c/example4.c`

  An example C program that uses a custom include function for processing wildcard includes. Note that this code will not compile on Windows.

Next: License, Previous: Example Programs, Up: libconfig [Contents][Index]

## 6 Other Bindings and Implementations

Various open-source libraries have been written that provide access to libconfig-style configuration files from other programming languages. Some of these libraries are wrappers which add new language bindings for libconfig while others are syntax-compatible reimplementations in other languages.

Here is a list of some of these implementations.

Next: D, Up: Other Bindings and Implementations [Contents][Index]

### 6.1 Bourne Shell

Łukasz A. Grabowski’s ls-config provides a means to read and write values in libconfig configuration files from Bourne shell scripts. The implementation is included in the libconfig git repository at https://github.com/hyperrealm/libconfig, in the `contrib/ls-config` subdirectory.

Next: Haskell, Previous: Bourne Shell, Up: Other Bindings and Implementations [Contents][Index]

### 6.2 D

Remi Thebault’s libconfig-d is a port of libconfig to the D programming language. It may be found at https://code.dlang.org/packages/libconfig-d.

Next: Java, Previous: D, Up: Other Bindings and Implementations [Contents][Index]

### 6.3 Haskell

Matthew Peddie’s libconfig provides Haskell bindings to libconfig. It may be found at https://hackage.haskell.org/package/libconfig.

Next: Lisp, Previous: Haskell, Up: Other Bindings and Implementations [Contents][Index]

### 6.4 Java

Andrey V. Pleskach has a pure-Java implementation of libconfig. It may be found on github at https://github.com/willyborankin/libconfig.

Next: Perl, Previous: Java, Up: Other Bindings and Implementations [Contents][Index]

### 6.5 Lisp

Oleg Shalaev’s cl-libconfig provides Common Lisp bindings for libconfig. It may be found on github at https://github.com/chalaev/cl-libconfig.

Next: Python, Previous: Lisp, Up: Other Bindings and Implementations [Contents][Index]

### 6.6 Perl

The Conf::Libconfig module provides Perl bindings for libconfig. It may be found on CPAN at http://search.cpan.org/~cnangel/Conf-Libconfig-0.05/ or on github at https://github.com/cnangel/Conf-Libconfig.

Next: Ruby, Previous: Perl, Up: Other Bindings and Implementations [Contents][Index]

### 6.7 Python

Heiner Tholen’s pylibconfig2 is a Python library that is syntax-compatible with libconfig. It may be found at https://pypi.python.org/pypi/pylibconfig2.

Christian Aichinger’s libconf is another pure-Python implementation with a more permissive license. It may be found at https://pypi.python.org/pypi/libconf or on github at https://github.com/Grk0/python-libconf.

The python-libconfig wrapper provides Python bindings to libconfig. It may be found on github at https://github.com/cnangel/python-libconfig/.

Next: Rust, Previous: Python, Up: Other Bindings and Implementations [Contents][Index]

### 6.8 Ruby

Christopher Mark Gore’s ruby-libconfig is a Ruby library that provides Ruby bindings for libconfig. It may be found at https://rubygems.org/gems/libconfig or on github at https://github.com/cgore/ruby-libconfig.

There is also another Ruby wrapper, libconfig-ruby, that is included in the libconfig git repository at https://github.com/hyperrealm/libconfig, in the `contrib/libconfig-ruby` subdirectory.

Previous: Ruby, Up: Other Bindings and Implementations [Contents][Index]

### 6.9 Rust

Ivan Semenkov’s librustconfig is a Rust library that provides Rust bindings for libconfig. It may be found on github at https://github.com/isemenkov/librustconfig.

Crate libconfig is a pure-Rust implementation of a configuration file parser that is compatible with the syntax of libconfig configuration files. It may be found at https://docs.rs/libconfig/latest/libconfig/.

Next: Configuration File Grammar, Previous: Other Bindings and Implementations, Up: libconfig [Contents][Index]

## Appendix A License

GNU LESSER GENERAL PUBLIC LICENSE
Version 2.1, February 1999

Copyright © 1991, 1999 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

[This is the first released version of the Lesser GPL. It also counts as the successor of the GNU Library Public License, version 2, hence the version number 2.1.]

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public Licenses are intended to guarantee your freedom to share and change free software–to make sure the software is free for all its users.

This license, the Lesser General Public License, applies to some specially designated software packages–typically libraries–of the Free Software Foundation and other authors who decide to use it. You can use it too, but we suggest you first think carefully about whether this license or the ordinary General Public License is the better strategy to use in any particular case, based on the explanations below.

When we speak of free software, we are referring to freedom of use, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish); that you receive source code or can get it if you want it; that you can change the software and use pieces of it in new free programs; and that you are informed that you can do these things.

To protect your rights, we need to make restrictions that forbid distributors to deny you these rights or to ask you to surrender these rights. These restrictions translate to certain responsibilities for you if you distribute copies of the library or if you modify it.

For example, if you distribute copies of the library, whether gratis or for a fee, you must give the recipients all the rights that we gave you. You must make sure that they, too, receive or can get the source code. If you link other code with the library, you must provide complete object files to the recipients, so that they can relink them with the library after making changes to the library and recompiling it. And you must show them these terms so they know their rights.

We protect your rights with a two-step method: (1) we copyright the library, and (2) we offer you this license, which gives you legal permission to copy, distribute and/or modify the library.

To protect each distributor, we want to make it very clear that there is no warranty for the free library. Also, if the library is modified by someone else and passed on, the recipients should know that what they have is not the original version, so that the original author’s reputation will not be affected by problems that might be introduced by others.

Finally, software patents pose a constant threat to the existence of any free program. We wish to make sure that a company cannot effectively restrict the users of a free program by obtaining a restrictive license from a patent holder. Therefore, we insist that any patent license obtained for a version of the library must be consistent with the full freedom of use specified in this license.

Most GNU software, including some libraries, is covered by the ordinary GNU General Public License. This license, the GNU Lesser General Public License, applies to certain designated libraries, and is quite different from the ordinary General Public License. We use this license for certain libraries in order to permit linking those libraries into non-free programs.

When a program is linked with a library, whether statically or using a shared library, the combination of the two is legally speaking a combined work, a derivative of the original library. The ordinary General Public License therefore permits such linking only if the entire combination fits its criteria of freedom. The Lesser General Public License permits more lax criteria for linking other code with the library.

We call this license the “Lesser” General Public License because it does Less to protect the user’s freedom than the ordinary General Public License. It also provides other free software developers Less of an advantage over competing non-free programs. These disadvantages are the reason we use the ordinary General Public License for many libraries. However, the Lesser license provides advantages in certain special circumstances.

For example, on rare occasions, there may be a special need to encourage the widest possible use of a certain library, so that it becomes a de-facto standard. To achieve this, non-free programs must be allowed to use the library. A more frequent case is that a free library does the same job as widely used non-free libraries. In this case, there is little to gain by limiting the free library to free software only, so we use the Lesser General Public License.

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Although the Lesser General Public License is Less protective of the users’ freedom, it does ensure that the user of a program that is linked with the Library has the freedom and the wherewithal to run that program using a modified version of the Library.

The precise terms and conditions for copying, distribution and modification follow. Pay close attention to the difference between a “work based on the library” and a “work that uses the library”. The former contains code derived from the library, whereas the latter must be combined with the library in order to run.

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How to Apply These Terms to Your New Libraries

If you develop a new library, and you want it to be of the greatest possible use to the public, we recommend making it free software that everyone can redistribute and change. You can do so by permitting redistribution under these terms (or, alternatively, under the terms of the ordinary General Public License).

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Also add information on how to contact you by electronic and paper mail.

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    <signature of Ty Coon>, 1 April 1990
    Ty Coon, President of Vice

That’s all there is to it!

Next: Function Index, Previous: License, Up: libconfig [Contents][Index]

## Appendix B Configuration File Grammar

Below is the BNF grammar for configuration files. Comments and include directives are not part of the grammar, so they are not included here.

    <configuration> ::=
          <setting-list>
        | <empty>

    <setting-list> ::=
          <setting>
        | <setting-list> <setting>

    <setting> ::=
          <name> ( ":" | "=" ) <value> ( ";" | "," | <empty> )

    <value> ::=
          <scalar-value>
        | <array>
        | <list>
        | <group>

    <value-list> ::=
          <value>
        | <value-list> "," <value>
        | <value-list> ","

    <scalar-value> ::=
          <boolean>
        | <integer>
        | <integer64>
        | <bin>
        | <bin64>
        | <oct>
        | <oct64>
        | <hex>
        | <hex64>
        | <float>
        | <string>

    <scalar-value-list> ::=
          <scalar-value>
        | <scalar-value-list> "," <scalar-value>
        | <scalar-value-list> ","

    <array> ::=
          "[" ( <scalar-value-list> | <empty> ) "]"

    <list> ::=
          "(" ( <value-list> | <empty> ) ")"

    <group> ::=
          "{" ( <setting-list> | <empty> ) "}"

    <empty> ::=

Terminals are defined below as regular expressions:

`<boolean>` | `([Tt][Rr][Uu][Ee])|([Ff][Aa][Ll][Ss][Ee])`
`<string>` | `\"([^\"\\]|\\.)*\"`
`<name>` | `[A-Za-z\*][-A-Za-z0-9_\*]*`
`<integer>` | `[-+]?[0-9]+`
`<integer64>` | `[-+]?[0-9]+L(L)?`
`<bin>` | `0[bB]([01]){1,32}`
`<bin64>` | `0[bB]([01]){1,64}L(L)?`
`<oct>` | `0[oOqQ]([0-7]){1,10}`
`<oct64>` | `0[oOqQ]([0-7]){1,21}L(L)?`
`<hex>` | `0[xX]([0-9A-Fa-f]){1,8}`
`<hex64>` | `0[xX]([0-9A-Fa-f]){1,16}L(L)?`
`<float>` | `([-+]?([0-9]*)?\.[0-9]*([eE][-+]?[0-9]+)?)|([-+]([0-9]+)(\.[0-9]*)?[eE][-+]?[0-9]+)`

Adjacent strings are automatically concatenated. Non-printable characters can be represented within strings using the escape sequence ‘`\x`’ followed by exactly two hex digits that represent the ASCII value as an 8-bit integer. The following escape sequences are also supported within strings, and have the conventional meanings: ‘`\"`’, ‘`\\`’, ‘`\a`’, ‘`\b`’, ‘`\f`’, ‘`\n`’, ‘`\r`’, ‘`\t`’, ‘`\v`’.

Next: Type Index, Previous: Configuration File Grammar, Up: libconfig [Contents][Index]

## Function Index

Jump to: | ~ A B C E F G I L O P R S W

| Index Entry |  | Section
~ |  |
| `~Config on Config`: |  | The C++ API
A |  |
| `add on Setting`: |  | The C++ API
| `add on Setting`: |  | The C++ API
| `add on Setting`: |  | The C++ API
B |  |
| `begin on Setting`: |  | The C++ API
| `begin on Setting`: |  | The C++ API
C |  |
| `clear on Config`: |  | The C++ API
| `Config on Config`: |  | The C++ API
| `config_clear`: |  | The C API
| `config_destroy`: |  | The C API
| `config_error_file`: |  | The C API
| `config_error_line`: |  | The C API
| `config_error_text`: |  | The C API
| `config_error_type`: |  | The C API
| `config_get_auto_convert`: |  | The C API
| `config_get_default_format`: |  | The C API
| `config_get_float_precision`: |  | The C API
| `config_get_hook`: |  | The C API
| `config_get_include_dir`: |  | The C API
| `config_get_option`: |  | The C API
| `config_get_options`: |  | The C API
| `config_get_tab_width`: |  | The C API
| `config_init`: |  | The C API
| `config_lookup`: |  | The C API
| `config_lookup_bool`: |  | The C API
| `config_lookup_const`: |  | The C API
| `config_lookup_float`: |  | The C API
| `config_lookup_int`: |  | The C API
| `config_lookup_int64`: |  | The C API
| `config_lookup_string`: |  | The C API
| `config_read`: |  | The C API
| `config_read_file`: |  | The C API
| `config_read_string`: |  | The C API
| `config_root_setting`: |  | The C API
| `config_setting_add`: |  | The C API
| `config_setting_get_bool`: |  | The C API
| `config_setting_get_bool_elem`: |  | The C API
| `config_setting_get_bool_safe`: |  | The C API
| `config_setting_get_elem`: |  | The C API
| `config_setting_get_float`: |  | The C API
| `config_setting_get_float_elem`: |  | The C API
| `config_setting_get_float_safe`: |  | The C API
| `config_setting_get_format`: |  | The C API
| `config_setting_get_hook`: |  | The C API
| `config_setting_get_int`: |  | The C API
| `config_setting_get_int64`: |  | The C API
| `config_setting_get_int64_elem`: |  | The C API
| `config_setting_get_int64_safe`: |  | The C API
| `config_setting_get_int_elem`: |  | The C API
| `config_setting_get_int_safe`: |  | The C API
| `config_setting_get_member`: |  | The C API
| `config_setting_get_string`: |  | The C API
| `config_setting_get_string_elem`: |  | The C API
| `config_setting_get_string_safe`: |  | The C API
| `config_setting_index`: |  | The C API
| `config_setting_is_aggregate`: |  | The C API
| `config_setting_is_array`: |  | The C API
| `config_setting_is_group`: |  | The C API
| `config_setting_is_list`: |  | The C API
| `config_setting_is_number`: |  | The C API
| `config_setting_is_root`: |  | The C API
| `config_setting_is_scalar`: |  | The C API
| `config_setting_length`: |  | The C API
| `config_setting_lookup`: |  | The C API
| `config_setting_lookup_bool`: |  | The C API
| `config_setting_lookup_const`: |  | The C API
| `config_setting_lookup_float`: |  | The C API
| `config_setting_lookup_int`: |  | The C API
| `config_setting_lookup_int64`: |  | The C API
| `config_setting_lookup_string`: |  | The C API
| `config_setting_name`: |  | The C API
| `config_setting_parent`: |  | The C API
| `config_setting_remove`: |  | The C API
| `config_setting_remove_elem`: |  | The C API
| `config_setting_set_bool`: |  | The C API
| `config_setting_set_bool_elem`: |  | The C API
| `config_setting_set_float`: |  | The C API
| `config_setting_set_float_elem`: |  | The C API
| `config_setting_set_format`: |  | The C API
| `config_setting_set_hook`: |  | The C API
| `config_setting_set_int`: |  | The C API
| `config_setting_set_int64`: |  | The C API
| `config_setting_set_int64_elem`: |  | The C API
| `config_setting_set_int_elem`: |  | The C API
| `config_setting_set_string`: |  | The C API
| `config_setting_set_string_elem`: |  | The C API
| `config_setting_source_file`: |  | The C API
| `config_setting_source_line`: |  | The C API
| `config_setting_type`: |  | The C API
| `config_set_auto_convert`: |  | The C API
| `config_set_default_format`: |  | The C API
| `config_set_destructor`: |  | The C API
| `config_set_fatal_error_func`: |  | The C API
| `config_set_float_precision`: |  | The C API
| `config_set_hook`: |  | The C API
| `config_set_include_dir`: |  | The C API
| `config_set_include_func`: |  | The C API
| `config_set_option`: |  | The C API
| `config_set_options`: |  | The C API
| `config_set_tab_width`: |  | The C API
| `config_write`: |  | The C API
| `config_write_file`: |  | The C API
| `c_str on Setting`: |  | The C++ API
E |  |
| `end on Setting`: |  | The C++ API
| `end on Setting`: |  | The C++ API
| `evaluateIncludePath on Config`: |  | The C++ API
| `exists on Config`: |  | The C++ API
| `exists on Config`: |  | The C++ API
| `exists on Setting`: |  | The C++ API
| `exists on Setting`: |  | The C++ API
F |  |
| `func`: |  | The C API
| `func`: |  | The C API
G |  |
| `getAutoConvert on Config`: |  | The C++ API
| `getDefaultFormat on Config`: |  | The C++ API
| `getError on ParseException`: |  | The C++ API
| `getFile on ParseException`: |  | The C++ API
| `getFloatPrecision on Config`: |  | The C++ API
| `getFormat on Setting`: |  | The C++ API
| `getIncludeDir on Config`: |  | The C++ API
| `getIndex on Setting`: |  | The C++ API
| `getLength on Setting`: |  | The C++ API
| `getLine on ParseException`: |  | The C++ API
| `getName on Setting`: |  | The C++ API
| `getOption on Config`: |  | The C++ API
| `getOptions on Config`: |  | The C++ API
| `getParent on Setting`: |  | The C++ API
| `getPath on Setting`: |  | The C++ API
| `getPath on SettingException`: |  | The C++ API
| `getRoot on Config`: |  | The C++ API
| `getSourceFile on Setting`: |  | The C++ API
| `getSourceLine on Setting`: |  | The C++ API
| `getTabWidth on Config`: |  | The C++ API
| `getType on Setting`: |  | The C++ API
I |  |
| `isAggregate on Setting`: |  | The C++ API
| `isArray on Setting`: |  | The C++ API
| `isGroup on Setting`: |  | The C++ API
| `isList on Setting`: |  | The C++ API
| `isNumber on Setting`: |  | The C++ API
| `isRoot on Setting`: |  | The C++ API
| `isScalar on Setting`: |  | The C++ API
| `isString on Setting`: |  | The C++ API
L |  |
| `LIBCONFIGXX_VER_MAJOR`: |  | Version Test Macros
| `LIBCONFIGXX_VER_MINOR`: |  | Version Test Macros
| `LIBCONFIGXX_VER_REVISION`: |  | Version Test Macros
| `LIBCONFIG_VER_MAJOR`: |  | Version Test Macros
| `LIBCONFIG_VER_MINOR`: |  | Version Test Macros
| `LIBCONFIG_VER_REVISION`: |  | Version Test Macros
| `lookup on Config`: |  | The C++ API
| `lookup on Config`: |  | The C++ API
| `lookup on Setting`: |  | The C++ API
| `lookup on Setting`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Config`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
| `lookupValue on Setting`: |  | The C++ API
O |  |
| `operator bool () on Setting`: |  | The C++ API
| `operator const char * () on Setting`: |  | The C++ API
| `operator double () on Setting`: |  | The C++ API
| `operator float () on Setting`: |  | The C++ API
| `operator int () on Setting`: |  | The C++ API
| `operator long () on Setting`: |  | The C++ API
| `operator long long () on Setting`: |  | The C++ API
| `operator std::string () on Setting`: |  | The C++ API
| `operator unsigned int () on Setting`: |  | The C++ API
| `operator unsigned long () on Setting`: |  | The C++ API
| `operator unsigned long long () on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator= on Setting`: |  | The C++ API
| `operator[] on Setting`: |  | The C++ API
| `operator[] on Setting`: |  | The C++ API
| `operator[] on Setting`: |  | The C++ API
P |  |
| `ParseException on ParseException`: |  | The C++ API
R |  |
| `read on Config`: |  | The C++ API
| `readFile on Config`: |  | The C++ API
| `readFile on Config`: |  | The C++ API
| `readString on Config`: |  | The C++ API
| `readString on Config`: |  | The C++ API
| `remove on Setting`: |  | The C++ API
| `remove on Setting`: |  | The C++ API
| `remove on Setting`: |  | The C++ API
S |  |
| `setAutoConvert on Config`: |  | The C++ API
| `setDefaultFormat on Config`: |  | The C++ API
| `setFloatPrecision on Config`: |  | The C++ API
| `setFormat on Setting`: |  | The C++ API
| `setIncludeDir on Config`: |  | The C++ API
| `setOption on Config`: |  | The C++ API
| `setOptions on Config`: |  | The C++ API
| `setTabWidth on Config`: |  | The C++ API
| `SettingNameException on SettingNameException`: |  | The C++ API
| `SettingNotFoundException on SettingNotFoundException`: |  | The C++ API
| `SettingNotFoundException on SettingNotFoundException`: |  | The C++ API
| `SettingNotFoundException on SettingNotFoundException`: |  | The C++ API
| `SettingRangeException on SettingRangeException`: |  | The C++ API
| `SettingRangeException on SettingRangeException`: |  | The C++ API
| `SettingRangeException on SettingRangeException`: |  | The C++ API
| `SettingTypeException on SettingTypeException`: |  | The C++ API
| `SettingTypeException on SettingTypeException`: |  | The C++ API
| `SettingTypeException on SettingTypeException`: |  | The C++ API
W |  |
| `write on Config`: |  | The C++ API
| `writeFile on Config`: |  | The C++ API
| `writeFile on Config`: |  | The C++ API

Jump to: | ~ A B C E F G I L O P R S W

Next: Concept Index, Previous: Function Index, Up: libconfig [Contents][Index]

## Type Index

Jump to: | C F P S

| Index Entry |  | Section
C |  |
| `Config`: |  | The C++ API
| `Config::Option`: |  | The C++ API
| `ConfigException`: |  | The C++ API
| `config_error_t`: |  | The C API
| `config_fatal_error_fn_t`: |  | The C API
| `config_include_fn_t`: |  | The C API
| `config_setting_t`: |  | The C API
| `config_t`: |  | The C API
F |  |
| `FileIOException`: |  | The C++ API
P |  |
| `ParseException`: |  | The C++ API
S |  |
| `Setting`: |  | The C++ API
| `Setting::Format`: |  | The C++ API
| `Setting::Type`: |  | The C++ API
| `SettingException`: |  | The C++ API
| `SettingNameException`: |  | The C++ API
| `SettingNotFoundException`: |  | The C++ API
| `SettingRangeException`: |  | The C++ API
| `SettingTypeException`: |  | The C++ API

Jump to: | C F P S

Previous: Type Index, Up: libconfig [Contents][Index]

## Concept Index

Jump to: | A B C D E F G H I L O P S U V

| Index Entry |  | Section
A |  |
| aggregate value: |  | The C API
| array: |  | Configuration Files
B |  |
| binary integer: |  | Integer Values
| boolean value: |  | Boolean Values
C |  |
| comment: |  | Comments
| configuration: |  | Configuration Files
D |  |
| decimal integer: |  | Integer Values
| destructor function: |  | The C API
E |  |
| escape sequence: |  | String Values
F |  |
| fatal error: |  | The C API
| floating point value: |  | Floating Point Values
| format: |  | The C API
G |  |
| group: |  | Configuration Files
H |  |
| hexadecimal integer: |  | Integer Values
| hook: |  | The C API
| hook: |  | The C API
I |  |
| include directive: |  | Include Directives
| include function: |  | Include Directives
L |  |
| list: |  | Configuration Files
| locale: |  | Internationalization Issues
O |  |
| octal integer: |  | Integer Values
P |  |
| path: |  | Configuration Files
| pkg-config: |  | Compiling Using pkg-config
S |  |
| scalar value: |  | Configuration Files
| setting: |  | Configuration Files
| string: |  | String Values
U |  |
| Unicode: |  | Internationalization Issues
| UTF-8: |  | Internationalization Issues
V |  |
| value: |  | Configuration Files

Jump to: | A B C D E F G H I L O P S U V