macros_misc.sgml

GLib是GTK+和GNOME工程的基础底层核心程序库

<!-- ##### 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>

<!-- ##### MACRO G_INLINE_FUNC ##### -->
<para>
Used to declare inline functions. If inline functions are not supported on
the particular platform, the macro evaluates to the empty string.
</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>

<!-- # Unused Parameters # -->
@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.
</para>

@macro_or_string: a macro or a string.


<!-- ##### 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 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_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_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 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_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_FUNCTION ##### -->
<para>
Expands to the GNU C <literal>__FUNCTION__</literal> variable if the 
compiler is <command>gcc</command>, or "" if it isn't. The GNU C 
<literal>__FUNCTION__</literal> variable contains the name of the 
current function. See the GNU C documentation for details. 
</para>



<!-- ##### MACRO G_GNUC_PRETTY_FUNCTION ##### -->
<para>
Expands to the GNU C <literal>__PRETTY_FUNCTION__</literal> variable 
if the compiler is <command>gcc</command>, or "" if it isn't.
The GNU C <literal>__PRETTY_FUNCTION__</literal> variable contains the 
name of the current function. For a C program this is the same as the 
<literal>__FUNCTION__</literal> variable but for C++ it also includes 
extra information such as the class and function prototype. See the 
GNU C documentation for details. 
</para>



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



<!-- ##### 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_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_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.
</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.
</para>
</note>