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@c attribute module documentation
@c Copyright 2020--2023 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.
@node Attributes
@section Attributes
@cindex Attributes
@findex __attribute__
This module provides a header file @file{attribute.h} that defines
macros related to C and C++ attributes and the GCC
@code{__attribute__} keyword.
Here is an example of its use:
@example
#include <attribute.h>
NODISCARD
extern char *crypt (char const *, char const *)
ATTRIBUTE_NOTHROW ATTRIBUTE_LEAF ATTRIBUTE_NONNULL ((1, 2));
@end example
@noindent
@code{NODISCARD} expands to @code{[[nodiscard]]} if the compiler
supports this C23 syntax, otherwise to
@code{__attribute__ ((__warn_unused_result__))} if the compiler
is a recent-enough GCC or GCC-like compiler, otherwise to nothing.
@code{ATTRIBUTE_NOTHROW} expands to @code{__attribute__
((__nothrow__))} if the compiler is a recent-enough GCC or GCC-like
compiler, and to nothing otherwise. Similarly for
@code{ATTRIBUTE_LEAF}. @code{ATTRIBUTE_NONNULL ((1, 2))} expands to
@code{__attribute__ ((__nonnull__ (1, 2)))} if the compiler is
recent-enough GCC, and to nothing otherwise.
Most of these attribute names begin with @code{ATTRIBUTE_}.
A few do not, because they are part of C23 and their
names are not likely to clash with other macro names.
These macros are @code{DEPRECATED}, @code{FALLTHROUGH},
@code{MAYBE_UNUSED}, and @code{NODISCARD}, which can
be defined to @code{[[deprecated]]} etc.@: on C23 platforms.
Also, these exceptional macros should be placed at the start of
function declarations, whereas the @code{ATTRIBUTE_*} macros can be
placed at the end.
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