gnu::warning(3attr) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| VERSIONS \| STANDARDS \| HISTORY \| CAVEATS \| EXAMPLES \| COLOPHON

gnu::warning(3attr)                                   gnu::warning(3attr)

NAME top

       gnu::warning, gnu::error - diagnose function calls not removed by
       optimizations

SYNOPSIS top

       [[gnu::warning(msg)]]
       [[gnu::error(msg)]]

DESCRIPTION top

       This attribute can be applied to a function.  If the function call
       is not removed by optimizations, a diagnostic is emitted.  The
       diagnostic contains the message msg and the location of the call
       in the source code.

       [[gnu::error()]] terminates the compilation after emitting the
       diagnostic.

VERSIONS top

       __attribute__((warning(msg)))
       __attribute__((error(msg)))

STANDARDS top

       GNU.

HISTORY top

       gcc 4.3, g++ 4.3, clang 14, clang++ 14.

CAVEATS top

       This diagnostic is emitted by the compiler, so it doesn't take
       into account linker optimizations.

EXAMPLES top

       #include <stdlib.h>

       [[gnu::warning("foo")]] void dontcall(void);

       int
       main(void)
       {
            dontcall();  // Warning.

            if (0)
                 dontcall();  // No warning.

            exit(EXIT_SUCCESS);
       }

COLOPHON top

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Linux man-pages 6.18            2025-11-11            gnu::warning(3attr)