# libconfig

A Library For Processing Structured Configuration Files
Version 1.3
6 April 2008
Mark A. Lindner

## Table of Contents

- libconfig
- 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 Compiling Using pkg-config
- 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
- 3 The C API
- 4 The C++ API
- 5 Configuration File Grammar
- Appendix A License
- Function Index
- Type Index
- Concept Index

Next: Introduction, Up: (dir)

## libconfig

Next: Configuration Files, Previous: Top, Up: Top

## 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 Linux, Solaris, and Mac OS X (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

### 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 38K for the C library and 66K for the C++ library) that is suitable for memory-constrained systems.
- Proper documentation.

Next: Using the Library from a C++ Program, Previous: Why Another Configuration File Library?, Up: Introduction

### 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.

Next: Multithreading Issues, Previous: Using the Library from a C Program, Up: Introduction

### 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.

Next: Compiling Using pkg-config, Previous: Using the Library from a C++ Program, Up: Introduction

### 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 these C library routines are cancel-safe or not depends on the host system.

Previous: Multithreading Issues, Up: Introduction

### 1.5 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 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.

Next: The C API, Previous: Introduction, Up: Top

## 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; } );

           misc:
           {
             pi = 3.141592654;
             bigint = 9223372036854775807L;
             columns = [ "Last Name", "First Name", "MI" ];
             bitmask = 0x1FC3;
           };
         };

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 either 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 conditions 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 types `long`, `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

### 2.1 Settings

A setting has the form:

name = value ;

or:

name : value ;

The trailing semicolon is required. 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

### 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.

Next: Lists, Previous: Groups, Up: Configuration Files

### 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.

Next: Integer Values, Previous: Arrays, Up: Configuration Files

### 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.

Next: 64-bit Integer Values, Previous: Lists, Up: Configuration Files

### 2.5 Integer Values

Integers can be represented in one of two ways: as a series of one or more decimal digits (``0`' - ``9`'), with an optional leading sign character (``+`' or ``-`'); or 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

### 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.

Next: Boolean Values, Previous: 64-bit Integer Values, Up: Configuration Files

### 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.

Next: String Values, Previous: Floating Point Values, Up: Configuration Files

### 2.8 Boolean Values

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

Next: Comments, Previous: Boolean Values, Up: Configuration Files

### 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`', and ``\t`' are also recognized, and have the usual meaning. 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."`

Previous: String Values, Up: Configuration Files

### 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.

Next: The C++ API, Previous: Configuration Files, Up: Top

## 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 config as a new, empty configuration.

> `config_destroy()` destroys the configuration config, deallocating all memory associated with the configuration, but not including the config_t structure itself.

— 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()` and `config_error_line()` 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: 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: int config_error_line (const config_t * config)

> These functions, which are implemented as macros, return the text and line number of the parse error, if one occurred during a call to `config_read()` or `config_read_file()`. Storage for the string returned by `config_error_text()` is managed by the library and released automatically when the configuration is destroyed; the string must not be freed by the caller.

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

> `config_set_auto_convert()` enables number auto-conversion for the configuration config if flag is non-zero, and disables it otherwise. 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 feature is disabled.

> `config_get_auto_convert()` returns `CONFIG_TRUE` if number auto-conversion is currently enabled for config; otherwise it returns `CONFIG_FALSE`.

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

> These functions locate the setting in the configuration config specified by the path path. They return the value of the setting on success, or a 0 or `NULL` value if the setting was not found or if the type of the value did not match the type requested.

> 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: long 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_set_int (config_setting_t * setting, long 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: short config_setting_get_format (config_setting_t * setting)
— Function: int config_setting_set_format (config_setting_t * setting, 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` or `CONFIG_FORMAT_HEX`. All settings support the `CONFIG_FORMAT_DEFAULT` format. The `CONFIG_FORMAT_HEX` format specifies hexadecimal formatting for integer values, and hence only applies to settings of type `CONFIG_TYPE_INT` and `CONFIG_TYPE_INT64`. If format is invalid for the given setting, it is ignored.

> `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 idx)

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

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

> These functions return the value at the specified index idx 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 idx 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 idx, long value)
— Function: config_setting_t * config_setting_set_int64_elem (config_setting_t * setting, int idx, long long value)
— Function: config_setting_t * config_setting_set_float_elem (config_setting_t * setting, int idx, double value)
— Function: config_setting_t * config_setting_set_bool_elem (config_setting_t * setting, int idx, int value)
— Function: config_setting_t * config_setting_set_string_elem (config_setting_t * setting, int idx, const char * value)

> These functions set the value at the specified index idx in the setting setting to value. If idx 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 idx 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.

— 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 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 idx)

> This function removes the child setting at the given index idx 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 idx is out of range, it returns `CONFIG_FALSE`.

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

> This function 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, 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: 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 parsed. This information is useful for reporting application-level errors. If the setting was not read from a file or stream, or if the line number is otherwise unavailable, the function returns 0.

— 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: Configuration File Grammar, Previous: The C API, Up: Top

## 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.

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

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

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

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

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

> 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 writeFile (const char * 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.

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

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

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

— Method on Config: void setAutoConvert (bool flag)
— Method on Config: bool getAutoConvert ()

> `setAutoConvert()` enables number auto-conversion for the configuration if flag is `true`, and disables it otherwise. When this feature is enabled, an attempt to assign a floating point setting to an integer (or vice versa), or assign an integer to a floating point setting (or vice versa) will cause the library to silently perform the necessary conversion (possibly leading to loss of data), rather than throwing a `SettingTypeException`. By default this feature is disabled.

> `getAutoConvert()` returns `true` if number auto-conversion is currently enabled for the configuration; otherwise it returns `false`.

— Method on Config: Setting & getRoot ()

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

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

> 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)
— Method on Config: bool exists (const char *path)

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

> 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++, i.e., if the first lookup fails (returning `false`), the remaining lookups are skipped entirely.

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

> 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, or unsigned long if it is of type `TypeInt`; `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`.

> 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");

> 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.

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

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

> A `Setting` object may be subscripted with an integer index idx if it is an array or list, or with either a string name or an integer index idx 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 (idx 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: bool lookupValue (const char *name, bool &value)
— Method on Setting: bool lookupValue (const std::string &name, bool &value)
— Method on Setting: bool lookupValue (const char *name, int &value)
— Method on Setting: bool lookupValue (const std::string &name, int &value)
— Method on Setting: bool lookupValue (const char *name, unsigned int &value)
— Method on Setting: bool lookupValue (const std::string &name, unsigned int &value)
— Method on Setting: bool lookupValue (const char *name, long long &value)
— Method on Setting: bool lookupValue (const std::string &name, long long &value)
— Method on Setting: bool lookupValue (const char *name, unsigned long long &value)
— Method on Setting: bool lookupValue (const std::string &name, unsigned long long &value)
— Method on Setting: bool lookupValue (const char *name, long &value)
— Method on Setting: bool lookupValue (const std::string &name, long &value)
— Method on Setting: bool lookupValue (const char *name, unsigned long &value)
— Method on Setting: bool lookupValue (const std::string &name, unsigned long &value)
— Method on Setting: bool lookupValue (const char *name, float &value)
— Method on Setting: bool lookupValue (const std::string &name, float &value)
— Method on Setting: bool lookupValue (const char *name, double &value)
— Method on Setting: bool lookupValue (const std::string &name, double &value)
— Method on Setting: bool lookupValue (const char *name, const char *&value)
— Method on Setting: bool lookupValue (const std::string &name, const char *&value)
— Method on Setting: bool lookupValue (const char *name, std::string &value)
— Method on Setting: bool lookupValue (const std::string &name, std::string &value)

> 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`, depending on the type.

> 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 idx)

> This method removes the child setting at the given index idx 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 idx is out of range, a `SettingNotFoundException` is thrown.

— Method on Setting: const char * getName ()

> 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 ()

> 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 ()

> 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 ()

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

— Method on Setting: int getIndex ()

> 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 ()

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

— Method on Setting: Setting::Format getFormat ()
— 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`, `FormatHex`. All settings support the `FormatDefault` format. The `FormatHex` format specifies hexadecimal formatting for integer values, and hence only applies 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)
— Method on Setting: bool exists (const char *name)

> 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: int getLength ()

> 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 ()
— Method on Setting: bool isArray ()
— Method on Setting: bool isList ()

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

— Method on Setting: bool isAggregate ()
— Method on Setting: bool isScalar ()
— Method on Setting: bool isNumber ()

> 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), and of a number (integer or floating point), respectively.

— Method on Setting: unsigned int getSourceLine ()

> This method returns the line number of the configuration file or stream at which the setting was parsed. This information is useful for reporting application-level errors. If the setting was not read from a file or stream, or if the line number is otherwise unavailable, the method returns 0.

Next: License, Previous: The C++ API, Up: Top

## 5 Configuration File Grammar

Below is the BNF grammar for configuration files. Comments are not part of the grammar, and hence are not included here.

         configuration = setting-list | empty

         empty =

         setting-list = setting | setting-list setting

         setting = name (":" | "=") value ";"

         value = scalar-value | array | list | group

         value-list = value | value-list "," value

         scalar-value = boolean | integer | integer64 | hex | hex64 | float
                        | string

         scalar-value-list = scalar-value | scalar-value-list "," scalar-value

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

         list = "(" (value-list | empty) ")"

         group = "{" (setting-list | 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)?`
`hex` | `0[Xx][0-9A-Fa-f]+`
`hex64` | `0[Xx][0-9A-Fa-f]+L(L)?`
`float` | `([-+]?([0-9]*)?\.[0-9]*([eE][-+]?[0-9]+)?)|([-+]([0-9]+)(\.[0-9]*)?[eE][-+]?[0-9]+)`

Next: Function Index, Previous: Configuration File Grammar, Up: Top

## 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

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11. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Library at all. For example, if a patent license would not permit royalty-free redistribution of the Library by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Library.

    If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply, and the section as a whole is intended to apply in other circumstances.

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    This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

12. If the distribution and/or use of the Library is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Library under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

13. The Free Software Foundation may publish revised and/or new versions of the Lesser General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

    Each version is given a distinguishing version number. If the Library specifies a version number of this License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Library does not specify a license version number, you may choose any version ever published by the Free Software Foundation.

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    NO WARRANTY

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END OF TERMS AND CONDITIONS

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).

To apply these terms, attach the following notices to the library. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

    <one line to give the library's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA

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

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the library, if necessary. Here is a sample; alter the names:

    Yoyodyne, Inc., hereby disclaims all copyright interest in the
    library `Frob' (a library for tweaking knobs) written by James Random Hacker.

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

That's all there is to it!

Next: Type Index, Previous: License, Up: Top

## Function Index

- `add on Setting`: The C++ API
- `Config on Config`: The C++ API
- `config_destroy`: The C API
- `config_error_line`: The C API
- `config_error_text`: The C API
- `config_get_auto_convert`: The C API
- `config_init`: The C API
- `config_lookup`: The C API
- `config_lookup_bool`: 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_root_setting`: The C API
- `config_set_auto_convert`: The C API
- `config_set_destructor`: 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_elem`: The C API
- `config_setting_get_float`: The C API
- `config_setting_get_float_elem`: 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_int_elem`: 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_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_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_line`: The C API
- `config_setting_type`: The C API
- `config_write`: The C API
- `config_write_file`: The C API
- `exists on Config`: The C++ API
- `exists on Setting`: The C++ API
- `getAutoConvert on Config`: The C++ API
- `getError on ParseException`: The C++ API
- `getFormat on Setting`: 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
- `getParent on Setting`: The C++ API
- `getPath on Setting`: The C++ API
- `getRoot on Config`: The C++ API
- `getSourceLine on Setting`: The C++ API
- `getType on Setting`: The C++ API
- `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
- `lookup on Config`: The C++ API
- `lookupValue on Config`: The C++ API
- `lookupValue on Setting`: The C++ API
- `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 long() on Setting`: The C++ API
- `operator 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 long() on Setting`: The C++ API
- `operator unsigned long() on Setting`: The C++ API
- `operator= on Setting`: The C++ API
- `operator[] on Setting`: The C++ API
- `read on Config`: The C++ API
- `readFile on Config`: The C++ API
- `remove on Setting`: The C++ API
- `setAutoConvert on Config`: The C++ API
- `setFormat on Setting`: The C++ API
- `write on Config`: The C++ API
- `writeFile on Config`: The C++ API
- `~Config on Config`: The C++ API

Next: Concept Index, Previous: Function Index, Up: Top

## Type Index

- `Config`: The C++ API
- `config_setting_t`: The C API
- `config_t`: The C API
- `ConfigException`: The C++ API
- `FileIOException`: The C++ API
- `ParseException`: The C++ API
- `Setting`: The C++ API
- `Setting::Format`: The C++ API
- `Setting::Type`: The C++ API
- `SettingFormat`: The C API
- `SettingNameException`: The C++ API
- `SettingNotFoundException`: The C++ API
- `SettingTypeException`: The C++ API

Previous: Type Index, Up: Top

## Concept Index

- array: Configuration Files
- configuration: Configuration Files
- group: Configuration Files
- list: Configuration Files
- path: Configuration Files
- scalar value: Configuration Files
- setting: Configuration Files
- value: Configuration Files