_Generic(3) — Linux manual page

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

_Generic(3)             Library Functions Manual             _Generic(3)

NAME top

       _Generic - type-generic selection

SYNOPSIS top

       _Generic(expression, type1: e1, ... /*, default: e */);

DESCRIPTION top

       _Generic() evaluates the path of code under the type selector
       that is compatible with the type of the controlling expression,
       or default: if no type is compatible.

       expression is not evaluated.

       This is especially useful for writing type-generic macros, that
       will behave differently depending on the type of the argument.

STANDARDS top

       C11.

HISTORY top

       C11.

EXAMPLES top

       The following program demonstrates how to write a replacement for
       the standard imaxabs(3) function, which being a function can't
       really provide what it promises: seamlessly upgrading to the
       widest available type.

              #include <stdint.h>
              #include <stdio.h>
              #include <stdlib.h>

              #define my_imaxabs  _Generic(INTMAX_C(0),  \
                  long:           labs,                  \
                  long long:      llabs                  \
              /*  long long long: lllabs */              \
              )

              int
              main(void)
              {
                  off_t  a;

                  a = -42;
                  printf("imaxabs(%jd) == %jd\n", (intmax_t) a, my_imaxabs(a));
                  printf("&imaxabs == %p\n", &my_imaxabs);
                  printf("&labs    == %p\n", &labs);
                  printf("&llabs   == %p\n", &llabs);

                  exit(EXIT_SUCCESS);
              }

COLOPHON top

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Linux man-pages 6.9.1          2024-06-15                    _Generic(3)