Next: Introduction, Up: (dir) [Contents][Index]
| • Introduction: | ||
| • Configuration Files: | ||
| • The C API: | ||
| • The C++ API: | ||
| • Example Programs: | ||
| • Configuration File Grammar: | ||
| • License: | ||
| • Function Index: | ||
| • Type Index: | ||
| • Concept Index: |
Next: Configuration Files, Previous: Top, Up: Top [Contents][Index]
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 [Contents][Index]
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:
Next: Using the Library from a C++ Program, Previous: Why Another Configuration File Library?, Up: Introduction [Contents][Index]
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 [Contents][Index]
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: Internationalization Issues, Previous: Using the Library from a C++ Program, Up: Introduction [Contents][Index]
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]
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]
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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The libconfig.h header declares the following macros:
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:
These macros represent the major version, minor version, and revision of the libconfig++ library.
Next: The C API, Previous: Introduction, Up: Top [Contents][Index]
| • Settings: | ||
| • Groups: | ||
| • Arrays: | ||
| • Lists: | ||
| • Integer Values: | ||
| • 64-bit Integer Values: | ||
| • Floating Point Values: | ||
| • Boolean Values: | ||
| • String Values: | ||
| • Comments: | ||
| • Include Directives: |
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:
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 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 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]
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]
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 [Contents][Index]
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 [Contents][Index]
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 [Contents][Index]
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 [Contents][Index]
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 [Contents][Index]
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 [Contents][Index]
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 [Contents][Index]
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.
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]
Three types of comments are allowed within a configuration:
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]
A configuration file may “include” the contents of another file using an include directive. This directive has the effect of inlining the contents of the named file at the point of inclusion.
An include directive must appear on its own line in the input. It has the form:
@include "filename"
Any backslashes or double quotes in the filename 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";
};
|
Include files may be nested to a maximum of 10 levels; exceeding this limit results in a parse error.
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: Top [Contents][Index]
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.
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.
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.
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.
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.
This function writes the configuration config to the given stream.
This function writes the configuration config to the file named
filename. It returns CONFIG_TRUE on success, or
CONFIG_FALSE on failure.
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.
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.
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.
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.
These functions, which are implemented as macros, set and get 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.
These functions, which are implemented as macros, set and get 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
This function returns the root setting for the configuration config. The root setting is a group.
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.
This function returns the parent setting of the given setting,
or NULL if setting is the root setting.
This function returns CONFIG_TRUE if the given setting is
the root setting, and CONFIG_FALSE otherwise.
This function returns the index of the given setting within its parent setting. If setting is the root setting, this function returns -1.
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.
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.
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.
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.
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.
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.
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.
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: Top [Contents][Index]
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.
SettingTypeException, SettingNotFoundException, and
SettingNameException all extend the common base
exception SettingException, which provides the following 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.
These methods create and destroy Config objects.
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.
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.
These methods read and parse a configuration from the string
str. A ParseException is thrown if a parse error occurs.
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.
setIncludeDir() 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.
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.
These methods set and get 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.
These methods set and get 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.
This method returns the root setting for the configuration, which is a group.
These methods locate the setting specified by the path path. If
the requested setting is not found, a SettingNotFoundException is
thrown.
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.
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.
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();
|
If the assignment is invalid due to a type mismatch, a
SettingTypeException is thrown.
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.
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.
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.
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.
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.
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.
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.
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.
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.
This method returns the parent setting of the setting. If the setting
is the root setting, a SettingNotFoundException is thrown.
This method returns true if the setting is the root setting, and
false otherwise.
This method returns the index of the setting within its parent setting. When applied to the root setting, this method returns -1.
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.
These methods get and set the external format for the setting.
The Setting::Format enumeration consists of the following
constants: FormatDefault and 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.
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.
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.
These convenience methods test if a setting is of a given type.
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, 64-bit integer, or floating point), respectively.
This function 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.
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.
Next: Configuration File Grammar, Previous: The C++ API, Up: Top [Contents][Index]
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:
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.
The C++ equivalent of example1.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.
The C++ equivalent of example2.c
An example C program that constructs a new configuration in memory and writes it to a file.
The C++ equivalent of example3.c
Next: License, Previous: Example Programs, Up: Top [Contents][Index]
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
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) "}"
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 [Contents][Index]
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.]
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That’s all there is to it!
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