l Libconfig is a simple library for processing structured configuration files.

l It is used for reading, manipulating, and writing structured configuration files

l It is more compact and more readable than XML. And unlike XML, it is type-aware, so it is not necessary to do string parsing in application code.

l The library includes bindings for both the C and C++ languages.

l The library features a fully reentrant parser and includes bindings for both the C and C++ programming languages.

l It works on POSIX-compliant UNIX and UNIX-like systems (GNU/Linux, Mac OS X, FreeBSD), Android, and Windows (2000, XP and later).

LICENSE-

Libconfig is distributed under the terms of the GNU Lesser General Public License. This license was chosen over the standard GNU license to allow libconfig to be used with non-free programs.

 HOW LIBCONFIG IS BETTER THAN OTHER LIBRARIES-

• It is a fully re-entrant parser. Independent configurations can be parsed in concurrent threads at the same time.
• It includes both C and C++ bindings, as well as hooks to allow for the creation of wrappers in other languages.
  
• It is 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.
  
• It is a low-footprint implementation (just 37K for the C library and 76K for the C++ library) that is suitable for memory-constrained systems.

USING LIBRARY FOR 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.

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:

l A scalar value: integer, 64-bit integer, floating-point number, boolean, or string.

l An array, which is a sequence of scalar values, all of which must have the same type.

l A group, which is a collection of settings.

l 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.

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.

THE C++ 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.

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:

 Likewise, there are various other methods which can be studied in depth.

DISADVANTAGES OF LIBCONFIG-

l The functions in the library do not make use of global variables and do not maintain state between successive calls.

l 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.

l Libconfig is not async-safe. Calls should not be made into the library from signal handlers.

l 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.

l Libconfig does not natively support Unicode configuration files.