path: root/docs/reference/glib/tmpl/macros_misc.sgml

<!-- ##### SECTION Title ##### -->
Miscellaneous Macros

<!-- ##### SECTION Short_Description ##### -->
specialized macros which are not used often

<!-- ##### SECTION Long_Description ##### -->
<para>
These macros provide more specialized features which are not needed so often
by application programmers.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### MACRO G_INLINE_FUNC ##### -->
<para>
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.
</para>
<para>
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.
</para>



<!-- ##### MACRO G_STMT_START ##### -->
<para>
Used within multi-statement macros so that they can be used in places where
only one statement is expected by the compiler.
</para>



<!-- ##### MACRO G_STMT_END ##### -->
<para>
Used within multi-statement macros so that they can be used in places where
only one statement is expected by the compiler.
</para>



<!-- ##### MACRO G_BEGIN_DECLS ##### -->
<para>
Used (along with #G_END_DECLS) to bracket header files. If the
compiler in use is a C++ compiler, adds <literal>extern "C"</literal> 
around the header.
</para>



<!-- ##### MACRO G_END_DECLS ##### -->
<para>
Used (along with #G_BEGIN_DECLS) to bracket header files. If the
compiler in use is a C++ compiler, adds <literal>extern "C"</literal> 
around the header.
</para>



<!-- ##### MACRO G_N_ELEMENTS ##### -->
<para>
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.
</para>

@arr: the array


<!-- ##### MACRO G_VA_COPY ##### -->
<para>
Portable way to copy <type>va_list</type> variables.
</para>
<para>
In order to use this function, you must include <filename>string.h</filename> 
yourself, because this macro may use <function>memmove()</function> and GLib 
does not include <function>string.h</function> for you.
</para>

@ap1: the <type>va_list</type> variable to place a copy of @ap2 in.
@ap2: a <type>va_list</type>.


<!-- ##### MACRO G_STRINGIFY ##### -->
<para>
Accepts a macro or a string and converts it into a string after
preprocessor argument expansion.
</para>

@macro_or_string: a macro or a string.


<!-- ##### MACRO G_PASTE ##### -->
<para>
Yields a new preprocessor pasted identifier 'identifier1identifier2'
from its expanded arguments 'identifier1' and 'identifier2'.
</para>

@identifier1: an identifier
@identifier2: an identifier
@Since: 2.20


<!-- ##### MACRO G_PASTE_ARGS ##### -->
<para>

</para>

@identifier1: 
@identifier2: 


<!-- ##### MACRO G_STATIC_ASSERT ##### -->
<para>
The G_STATIC_ASSERT macro lets the programmer check a condition at compile time,
the condition needs to be compile time computable.
The macro can be used in any place where a <literal>typedef</literal> is valid.
The macro should only be used once per source code line.
</para>

@expr: a constant expression.
@Since: 2.20


<!-- ##### MACRO G_GNUC_EXTENSION ##### -->
<para>
Expands to <literal>__extension__</literal> when <command>gcc</command> is 
used as the compiler.
This simply tells <command>gcc</command> not to warn about the following non-standard code
when compiling with the <option>-pedantic</option> option.
</para>



<!-- ##### MACRO G_GNUC_CONST ##### -->
<para>
Expands to the GNU C <literal>const</literal> function attribute if the compiler is 
<command>gcc</command>. 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. 
</para>
<note><para>
A function that has pointer arguments and examines the data pointed to 
must <emphasis>not</emphasis> 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.
</para></note>



<!-- ##### MACRO G_GNUC_PURE ##### -->
<para>
Expands to the GNU C <literal>pure</literal> function attribute if the compiler is 
<command>gcc</command>. 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. 
</para>



<!-- ##### MACRO G_GNUC_MALLOC ##### -->
<para>
Expands to the GNU C <literal>malloc</literal> function attribute if the 
compiler is <command>gcc</command>. 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. 
</para>

@Since: 2.6


<!-- ##### MACRO G_GNUC_ALLOC_SIZE ##### -->
<para>
Expands to the GNU C <literal>alloc_size</literal> function attribute if the 
compiler is a new enough <command>gcc</command>. 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. 
</para>

@x: the index of the argument specifying the allocation size
@Since: 2.18


<!-- ##### MACRO G_GNUC_ALLOC_SIZE2 ##### -->
<para>
Expands to the GNU C <literal>alloc_size</literal> function attribute if the 
compiler is a new enough <command>gcc</command>. 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. 
</para>

@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


<!-- ##### MACRO G_GNUC_DEPRECATED ##### -->
<para>
Expands to the GNU C <literal>deprecated</literal> attribute if the compiler 
is <command>gcc</command>.
It can be used to mark typedefs, variables and functions as deprecated. 
When called with the <option>-Wdeprecated</option> option, the compiler will 
generate warnings when deprecated interfaces are used.
See the GNU C documentation for details. 
</para>

@Since: 2.2


<!-- ##### MACRO G_GNUC_NORETURN ##### -->
<para>
Expands to the GNU C <literal>noreturn</literal> function attribute if the 
compiler is <command>gcc</command>. 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. 
</para>



<!-- ##### MACRO G_GNUC_UNUSED ##### -->
<para>
Expands to the GNU C <literal>unused</literal> function attribute if the compiler is 
<command>gcc</command>. It is used for declaring functions which may never be used.
It avoids possible compiler warnings. See the GNU C documentation for details. 
</para>



<!-- ##### MACRO G_GNUC_PRINTF ##### -->
<para>
Expands to the GNU C <literal>format</literal> function attribute if the compiler is 
<command>gcc</command>. This is used for declaring functions which take a variable number of
arguments, with the same syntax as <function>printf()</function>.
It allows the compiler to type-check the arguments passed to the function.
See the GNU C documentation for details. 
</para>
<informalexample><programlisting>
gint g_snprintf (gchar  *string,
                 gulong       n,
                 gchar const *format,
                 ...) G_GNUC_PRINTF (3, 4);
</programlisting></informalexample>

@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.


<!-- ##### MACRO G_GNUC_SCANF ##### -->
<para>
Expands to the GNU C <literal>format</literal> function attribute if the compiler is <command>gcc</command>.
This is used for declaring functions which take a variable number of
arguments, with the same syntax as <function>scanf()</function>.
It allows the compiler to type-check the arguments passed to the function.
See the GNU C documentation for details. 
</para>

@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.


<!-- ##### MACRO G_GNUC_FORMAT ##### -->
<para>
Expands to the GNU C <literal>format_arg</literal> function attribute if the compiler is <command>gcc</command>.
This function attribute specifies that a function takes a format
string for a <function>printf()</function>, <function>scanf()</function>, 
<function>strftime()</function> or <function>strfmon()</function> style
function and modifies it, so that the result can be passed to a 
<function>printf()</function>, <function>scanf()</function>, 
<function>strftime()</function> or <function>strfmon()</function> 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. 
</para>
<informalexample><programlisting>
gchar *g_dgettext (gchar *domain_name, gchar *msgid) G_GNUC_FORMAT (2);
</programlisting></informalexample>

@arg_idx: the index of the argument.


<!-- ##### MACRO G_GNUC_NULL_TERMINATED ##### -->
<para>
Expands to the GNU C <literal>sentinel</literal> function attribute if the 
compiler is <command>gcc</command>, 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. 
</para>

Since: 2.8



<!-- ##### MACRO G_GNUC_WARN_UNUSED_RESULT ##### -->
<para>
Expands to the GNU C <literal>warn_unused_result</literal> function attribute 
if the compiler is <command>gcc</command>, 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. 
</para>

@Since: 2.10


<!-- ##### MACRO G_GNUC_FUNCTION ##### -->
<para>
Expands to "" on all modern compilers, and to <literal>__FUNCTION__</literal>
on <command>gcc</command> version 2.x. Don't use it.
</para>

@Deprecated: 2.16


<!-- ##### MACRO G_GNUC_PRETTY_FUNCTION ##### -->
<para>
Expands to "" on all modern compilers, and to 
<literal>__PRETTY_FUNCTION__</literal> on <command>gcc</command> version 2.x. 
Don't use it.
</para>

@Deprecated: 2.16


<!-- ##### MACRO G_GNUC_NO_INSTRUMENT ##### -->
<para>
Expands to the GNU C <literal>no_instrument_function</literal> function 
attribute if the compiler is <command>gcc</command>. Functions with this 
attribute will not be 
instrumented for profiling, when the compiler is called with the
<option>-finstrument-functions</option> option.
See the GNU C documentation for details. 
</para>



<!-- ##### MACRO G_HAVE_GNUC_VISIBILITY ##### -->
<para>
This macro is defined as 1 if the compiler supports ELF visibility 
attributes (currently only <command>gcc</command>).
</para>

Since: 2.6



<!-- ##### MACRO G_GNUC_INTERNAL ##### -->
<para>
This attribute can be used for marking library functions as being used 
internally to the library only, which may allow the compiler to handle
function calls more efficiently. 
Note that static functions do not need to be marked as internal in this way. 
See the GNU C documentation for details. 
</para>
<para>
When using a compiler that supports the GNU C hidden visibility attribute, 
this macro expands to <literal>__attribute__((visibility("hidden")))</literal>.
When using the Sun Studio compiler, it expands to <literal>__hidden</literal>.
</para>
<para>
Note that for portability, the attribute should be placed before the
function declaration. While GCC allows the macro after the declaration, 
Sun Studio does not.
</para>
<informalexample><programlisting>
G_GNUC_INTERNAL
void _g_log_fallback_handler (const gchar    *log_domain,
                              GLogLevelFlags  log_level,
                              const gchar    *message,
                              gpointer        unused_data);
</programlisting></informalexample>

Since: 2.6



<!-- ##### MACRO G_GNUC_MAY_ALIAS ##### -->
<para>
Expands to the GNU C <literal>may_alias</literal> type attribute 
if the compiler is <command>gcc</command>. 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. 
</para>

Since: 2.14



<!-- ##### FUNCTION G_LIKELY ##### -->
<para>
Hints the compiler that the expression is likely to evaluate to a true
value. The compiler may use this information for optimizations.
</para>
<informalexample><programlisting>
if (G_LIKELY (random () != 1))
  g_print ("not one");
</programlisting></informalexample>

@Returns: the value of @expr
@Since: 2.2
<!-- # Unused Parameters # -->
@expr: the expression


<!-- ##### MACRO G_UNLIKELY ##### -->
<para>
Hints the compiler that the expression is unlikely to evaluate to a true
value. The compiler may use this information for optimizations.
</para>
<informalexample><programlisting>
if (G_UNLIKELY (random () == 1))
  g_print ("a random one");
</programlisting></informalexample>

@expr: the expression
@Returns: the value of @expr
@Since: 2.2


<!-- ##### MACRO G_STRLOC ##### -->
<para>
Expands to a string identifying the current code position. 
</para>



<!-- ##### MACRO G_STRFUNC ##### -->
<para>
Expands to a string identifying the current function. 
</para>

@Since: 2.4


<!-- ##### MACRO G_GINT16_MODIFIER ##### -->
<para>
The platform dependent length modifier for constructing printf() conversion
specifiers for values of type #gint16 or #guint16. It is a string literal, 
but doesn't include the percent-sign, such that you can add precision and 
length modifiers between percent-sign and conversion specifier and append a 
conversion specifier.
</para>

<para>
The following example prints "0x7b";
<informalexample>
<programlisting>
gint16 value = 123;
g_print ("%#" G_GINT16_MODIFIER "x", value);
</programlisting>
</informalexample>
</para>

@Since: 2.4


<!-- ##### MACRO G_GINT16_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #gint16. It is a string literal, but doesn't
include the percent-sign, such that you can add precision and length
modifiers between percent-sign and conversion specifier.
</para>

<para>
<informalexample>
<programlisting>
gint16 in;
gint32 out;
sscanf ("42", "%" G_GINT16_FORMAT, &amp;in)
out = in * 1000;
g_print ("%" G_GINT32_FORMAT, out);
</programlisting>
</informalexample>
</para>



<!-- ##### MACRO G_GUINT16_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #guint16. See also #G_GINT16_FORMAT.
</para>



<!-- ##### MACRO G_GINT32_MODIFIER ##### -->
<para>
The platform dependent length modifier for constructing printf() conversion
specifiers for values of type #gint32 or #guint32. See also #G_GINT16_MODIFIER.
</para>

@Since: 2.4


<!-- ##### MACRO G_GINT32_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #gint32. See also #G_GINT16_FORMAT.
</para>



<!-- ##### MACRO G_GUINT32_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #guint32. See also #G_GINT16_FORMAT.
</para>



<!-- ##### MACRO G_GINT64_MODIFIER ##### -->
<para>
The platform dependent length modifier for constructing printf() conversion
specifiers for values of type #gint64 or #guint64. See also #G_GINT16_MODIFIER.
</para>

<note>
<para>
Some platforms do not support printing 64 bit integers,
even though the types are supported. On such platforms #G_GINT64_MODIFIER
is not defined.
</para>
</note>

@Since: 2.4


<!-- ##### MACRO G_GINT64_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #gint64. See also #G_GINT16_FORMAT.
</para>

<note>
<para>
Some platforms do not support scanning and printing 64 bit integers,
even though the types are supported. On such platforms #G_GINT64_FORMAT
is not defined. Note that scanf() may not support 64 bit integers, even
if #G_GINT64_FORMAT is defined. Due to its weak error handling, scanf() is not 
recommended for parsing anyway; consider using g_strtoull() instead.
</para>
</note>



<!-- ##### MACRO G_GUINT64_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #guint64. See also #G_GINT16_FORMAT.
</para>

<note>
<para>
Some platforms do not support scanning and printing 64 bit integers,
even though the types are supported. On such platforms #G_GUINT64_FORMAT
is not defined.  Note that scanf() may not support 64 bit integers, even
if #G_GINT64_FORMAT is defined. Due to its weak error handling, scanf() is not 
recommended for parsing anyway; consider using g_strtoull() instead.
</para>
</note>



<!-- ##### MACRO G_GSIZE_MODIFIER ##### -->
<para>
The platform dependent length modifier for constructing printf() conversion
specifiers for values of type #gsize or #gssize. See also #G_GINT16_MODIFIER.
</para>

@Since: 2.6


<!-- ##### MACRO G_GSIZE_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #gsize. See also #G_GINT16_FORMAT.
</para>

@Since: 2.6


<!-- ##### MACRO G_GSSIZE_FORMAT ##### -->
<para>
This is the platform dependent conversion specifier for scanning and
printing values of type #gssize. See also #G_GINT16_FORMAT.
</para>

@Since: 2.6