Macro: qef_c_noreturn

Back to the Main Page. | Download the M4 Source.

# qef_c_noreturn

## Synopsis

`QEF_C_NORETURN`

## Version

1.1.1.1 (2001/07/26) Miscellaneous @ ac-archive-0.5.32

## Author

Geoff Richards <ctzgpr@scs.leeds.ac.uk>

## Description

Check if we can use GCC's __noreturn__ attribute in prototypes to indicate that functions never return. This can be used by the compiler to do some extra optimizations.

FUNCATTR_NORETURN is defined as what we should put at the end of function prototypes to achieve this. If the compiler doesn't support it then it is defined as empty.

An example of a a function's prototype and implementation using this macro:

`void this_function_never_returns (void) FUNCATTR_NORETURN;`

`void this_function_never_returns (void) {`
`exit (0);`
`}`

## M4 Source Code

    AC_DEFUN([QEF_C_NORETURN],
    [AC_REQUIRE([AC_PROG_CC])
    AC_MSG_CHECKING(whether the C compiler (${CC-cc}) accepts noreturn attribute)
    AC_CACHE_VAL(qef_cv_c_noreturn,
    [qef_cv_c_noreturn=no
    AC_TRY_COMPILE(
    [#include <stdio.h>
    void f (void) __attribute__ ((noreturn));
    void f (void)
    {
       exit (1);
    }
    ], [
       f ();
    ],
    [qef_cv_c_noreturn="yes";  FUNCATTR_NORETURN_VAL="__attribute__ ((noreturn))"],
    [qef_cv_c_noreturn="no";   FUNCATTR_NORETURN_VAL="/* will not return */"])
    ])

    AC_MSG_RESULT($qef_cv_c_noreturn)
    AC_DEFINE_UNQUOTED(FUNCATTR_NORETURN, $FUNCATTR_NORETURN_VAL)
    ])dnl