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

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

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

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

STANDARDS
       GNU.

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

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

EXAMPLES
       #include <stdlib.h>

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

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

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

            exit(EXIT_SUCCESS);
       }

Linux man-pages 6.17              2025-11-11               gnu::warning(3attr)