## Miscellaneous Macros Miscellaneous Macros — specialized macros which are not used often |

## Synopsis

    #include <glib.h>

    #define             G_INLINE_FUNC

    #define             G_STMT_START
    #define             G_STMT_END

    #define             G_BEGIN_DECLS
    #define             G_END_DECLS

    #define             G_N_ELEMENTS                        (arr)

    #define             G_VA_COPY                           (ap1,ap2)

    #define             G_STRINGIFY                         (macro_or_string)

    #define             G_GNUC_EXTENSION
    #define             G_GNUC_CONST
    #define             G_GNUC_PURE
    #define             G_GNUC_MALLOC
    #define             G_GNUC_ALLOC_SIZE                   (x)
    #define             G_GNUC_ALLOC_SIZE2                  (x,y)
    #define             G_GNUC_DEPRECATED
    #define             G_GNUC_NORETURN
    #define             G_GNUC_UNUSED
    #define             G_GNUC_PRINTF                       ( format_idx, arg_idx )
    #define             G_GNUC_SCANF                        ( format_idx, arg_idx )
    #define             G_GNUC_FORMAT                       ( arg_idx )
    #define             G_GNUC_NULL_TERMINATED
    #define             G_GNUC_WARN_UNUSED_RESULT
    #define             G_GNUC_FUNCTION
    #define             G_GNUC_PRETTY_FUNCTION
    #define             G_GNUC_NO_INSTRUMENT
    #define             G_GNUC_MAY_ALIAS

    if                  G_LIKELY                            ();
    #define             G_UNLIKELY                          (expr)

    #define             G_STRLOC
    #define             G_STRFUNC

## Description

These macros provide more specialized features which are not needed so often by application programmers.

## Details

### G_INLINE_FUNC

    #define             G_INLINE_FUNC

This macro is used to export function prototypes so they can be linked with an external version when no inlining is performed. The file which implements the functions should define `G_IMPLEMENTS_INLINES` before including the headers which contain `G_INLINE_FUNC` declarations. Since inlining is very compiler-dependent using these macros correctly is very difficult. Their use is strongly discouraged.

This macro is often mistaken for a replacement for the inline keyword; inline is already declared in a portable manner in the glib headers and can be used normally.

### G_STMT_START

    #  define G_STMT_START  do

Used within multi-statement macros so that they can be used in places where only one statement is expected by the compiler.

### G_STMT_END

    #  define G_STMT_END    while (0)

Used within multi-statement macros so that they can be used in places where only one statement is expected by the compiler.

### G_BEGIN_DECLS

    #define             G_BEGIN_DECLS

Used (along with G_END_DECLS) to bracket header files. If the compiler in use is a C++ compiler, adds `extern "C"` around the header.

### G_END_DECLS

    #define             G_END_DECLS

Used (along with G_BEGIN_DECLS) to bracket header files. If the compiler in use is a C++ compiler, adds `extern "C"` around the header.

### G_N_ELEMENTS()

    #define G_N_ELEMENTS(arr)		(sizeof (arr) / sizeof ((arr)[0]))

Determines the number of elements in an array. The array must be declared so the compiler knows its size at compile-time; this macro will not work on an array allocated on the heap, only static arrays or arrays on the stack.

`arr` : | the array

### G_VA_COPY()

    #define             G_VA_COPY(ap1,ap2)

Portable way to copy va_list variables.

In order to use this function, you must include `string.h` yourself, because this macro may use ``memmove()`` and GLib does not include `string.h` for you.

`ap1` : | the va_list variable to place a copy of `ap2` in.
`ap2` : | a va_list.

### G_STRINGIFY()

    #define G_STRINGIFY(macro_or_string)	G_STRINGIFY_ARG (macro_or_string)

Accepts a macro or a string and converts it into a string.

`macro_or_string` : | a macro or a string.

### G_GNUC_EXTENSION

    #define             G_GNUC_EXTENSION

Expands to `__extension__` when gcc is used as the compiler. This simply tells gcc not to warn about the following non-standard code when compiling with the `-pedantic` option.

### G_GNUC_CONST

    #define             G_GNUC_CONST

Expands to the GNU C `const` function attribute if the compiler is gcc. Declaring a function as const enables better optimization of calls to the function. A const function doesn't examine any values except its parameters, and has no effects except its return value. See the GNU C documentation for details.

### Note

A function that has pointer arguments and examines the data pointed to must not be declared const. Likewise, a function that calls a non-const function usually must not be const. It doesn't make sense for a const function to return void.

### G_GNUC_PURE

    #define             G_GNUC_PURE

Expands to the GNU C `pure` function attribute if the compiler is gcc. Declaring a function as pure enables better optimization of calls to the function. A pure function has no effects except its return value and the return value depends only on the parameters and/or global variables. See the GNU C documentation for details.

### G_GNUC_MALLOC

    #define             G_GNUC_MALLOC

Expands to the GNU C `malloc` function attribute if the compiler is gcc. Declaring a function as malloc enables better optimization of the function. A function can have the malloc attribute if it returns a pointer which is guaranteed to not alias with any other pointer when the function returns (in practice, this means newly allocated memory). See the GNU C documentation for details.

Since 2.6

### G_GNUC_ALLOC_SIZE()

    #define             G_GNUC_ALLOC_SIZE(x)

Expands to the GNU C `alloc_size` function attribute if the compiler is a new enough gcc. This attribute tells the compiler that the function returns a pointer to memory of a size that is specified by the `x`th function parameter. See the GNU C documentation for details.

`x` : | the index of the argument specifying the allocation size

Since 2.18

### G_GNUC_ALLOC_SIZE2()

    #define             G_GNUC_ALLOC_SIZE2(x,y)

Expands to the GNU C `alloc_size` function attribute if the compiler is a new enough gcc. This attribute tells the compiler that the function returns a pointer to memory of a size that is specified by the product of two function parameters. See the GNU C documentation for details.

`x` : | the index of the argument specifying one factor of the allocation size
`y` : | the index of the argument specifying the second factor of the allocation size

Since 2.18

### G_GNUC_DEPRECATED

    #define             G_GNUC_DEPRECATED

Expands to the GNU C `deprecated` attribute if the compiler is gcc. It can be used to mark typedefs, variables and functions as deprecated. When called with the `-Wdeprecated` option, the compiler will generate warnings when deprecated interfaces are used. See the GNU C documentation for details.

Since 2.2

### G_GNUC_NORETURN

    #define             G_GNUC_NORETURN

Expands to the GNU C `noreturn` function attribute if the compiler is gcc. It is used for declaring functions which never return. It enables optimization of the function, and avoids possible compiler warnings. See the GNU C documentation for details.

### G_GNUC_UNUSED

    #define             G_GNUC_UNUSED

Expands to the GNU C `unused` function attribute if the compiler is gcc. It is used for declaring functions which may never be used. It avoids possible compiler warnings. See the GNU C documentation for details.

### G_GNUC_PRINTF()

    #define             G_GNUC_PRINTF( format_idx, arg_idx )

Expands to the GNU C `format` function attribute if the compiler is gcc. This is used for declaring functions which take a variable number of arguments, with the same syntax as ``printf()``. It allows the compiler to type-check the arguments passed to the function. See the GNU C documentation for details.

    gint g_snprintf (gchar  *string,
                     gulong       n,
                     gchar const *format,
                     ...) G_GNUC_PRINTF (3, 4);

`format_idx` : | the index of the argument corresponding to the format string. (The arguments are numbered from 1).
`arg_idx` : | the index of the first of the format arguments.

### G_GNUC_SCANF()

    #define             G_GNUC_SCANF( format_idx, arg_idx )

Expands to the GNU C `format` function attribute if the compiler is gcc. This is used for declaring functions which take a variable number of arguments, with the same syntax as ``scanf()``. It allows the compiler to type-check the arguments passed to the function. See the GNU C documentation for details.

`format_idx` : | the index of the argument corresponding to the format string. (The arguments are numbered from 1).
`arg_idx` : | the index of the first of the format arguments.

### G_GNUC_FORMAT()

    #define             G_GNUC_FORMAT( arg_idx )

Expands to the GNU C `format_arg` function attribute if the compiler is gcc. This function attribute specifies that a function takes a format string for a ``printf()``, ``scanf()``, ``strftime()`` or ``strfmon()`` style function and modifies it, so that the result can be passed to a ``printf()``, ``scanf()``, ``strftime()`` or ``strfmon()`` style function (with the remaining arguments to the format function the same as they would have been for the unmodified string). See the GNU C documentation for details.

    gchar *g_dgettext (gchar *domain_name, gchar *msgid) G_GNUC_FORMAT (2);

`arg_idx` : | the index of the argument.

### G_GNUC_NULL_TERMINATED

    #define             G_GNUC_NULL_TERMINATED

Expands to the GNU C `sentinel` function attribute if the compiler is gcc, or "" if it isn't. This function attribute only applies to variadic functions and instructs the compiler to check that the argument list is terminated with an explicit `NULL`. See the GNU C documentation for details.

Since: 2.8

### G_GNUC_WARN_UNUSED_RESULT

    #define             G_GNUC_WARN_UNUSED_RESULT

Expands to the GNU C `warn_unused_result` function attribute if the compiler is gcc, or "" if it isn't. This function attribute makes the compiler emit a warning if the result of a function call is ignored. See the GNU C documentation for details.

Since 2.10

### G_GNUC_FUNCTION

    #define             G_GNUC_FUNCTION

### Warning

`G_GNUC_FUNCTION` is deprecated and should not be used in newly-written code. 2.16

Expands to "" on all modern compilers, and to `__FUNCTION__` on gcc version 2.x. Don't use it.

### G_GNUC_PRETTY_FUNCTION

    #define             G_GNUC_PRETTY_FUNCTION

### Warning

`G_GNUC_PRETTY_FUNCTION` is deprecated and should not be used in newly-written code. 2.16

Expands to "" on all modern compilers, and to `__PRETTY_FUNCTION__` on gcc version 2.x. Don't use it.

### G_GNUC_NO_INSTRUMENT

    #define             G_GNUC_NO_INSTRUMENT

Expands to the GNU C `no_instrument_function` function attribute if the compiler is gcc. Functions with this attribute will not be instrumented for profiling, when the compiler is called with the `-finstrument-functions` option. See the GNU C documentation for details.

### G_GNUC_MAY_ALIAS

    #define             G_GNUC_MAY_ALIAS

Expands to the GNU C `may_alias` type attribute if the compiler is gcc. Types with this attribute will not be subjected to type-based alias analysis, but are assumed to alias with any other type, just like char. See the GNU C documentation for details.

Since: 2.14

### G_LIKELY ()

    if                  G_LIKELY                            ();

Hints the compiler that the expression is likely to evaluate to a true value. The compiler may use this information for optimizations.

    if (G_LIKELY (random () != 1))
      g_print ("not one");

Returns : | the value of `expr`

Since 2.2

### G_UNLIKELY()

    #define             G_UNLIKELY(expr)

Hints the compiler that the expression is unlikely to evaluate to a true value. The compiler may use this information for optimizations.

    if (G_UNLIKELY (random () == 1))
      g_print ("a random one");

`expr` : | the expression
Returns : | the value of `expr`

Since 2.2

### G_STRLOC

    #define             G_STRLOC

Expands to a string identifying the current code position.

### G_STRFUNC

    #define             G_STRFUNC

Expands to a string identifying the current function.

Since 2.4