1_Generic(3)                Library Functions Manual                _Generic(3)
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NAME

6       _Generic - type-generic selection
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SYNOPSIS

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

12       _Generic()  evaluates  the path of code under the type selector that is
13       compatible with the type of the controlling expression, or default:  if
14       no type is compatible.
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16       expression is not evaluated.
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18       This  is  especially  useful for writing type-generic macros, that will
19       behave differently depending on the type of the argument.
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STANDARDS

22       C11.
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HISTORY

25       C11.
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EXAMPLES

28       The following program demonstrates how to write a replacement  for  the
29       standard  imaxabs(3) function, which being a function can't really pro‐
30       vide what it promises: seamlessly upgrading  to  the  widest  available
31       type.
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33              #include <stdint.h>
34              #include <stdio.h>
35              #include <stdlib.h>
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37              #define my_imaxabs  _Generic(INTMAX_C(0),  \
38                  long:           labs,                  \
39                  long long:      llabs                  \
40               /* long long long: lllabs */              \
41              )
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43              int
44              main(void)
45              {
46                  off_t  a;
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48                  a = -42;
49                  printf("imaxabs(%jd) == %jd\n", (intmax_t) a, my_imaxabs(a));
50                  printf("&imaxabs == %p\n", &my_imaxabs);
51                  printf("&labs    == %p\n", &labs);
52                  printf("&llabs   == %p\n", &llabs);
53
54                  exit(EXIT_SUCCESS);
55              }
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59Linux man-pages 6.04              2023-03-30                       _Generic(3)