confstr(3)

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

6       confstr - get configuration dependent string variables
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <unistd.h>
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14       size_t confstr(int name, char buf[.size], size_t size);
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16   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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18       confstr():
19           _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
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DESCRIPTION

22       confstr() gets the value of configuration-dependent string variables.
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24       The  name argument is the system variable to be queried.  The following
25       variables are supported:
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27       _CS_GNU_LIBC_VERSION (GNU C library only; since glibc 2.3.2)
28              A string which identifies the GNU C library version on this sys‐
29              tem (e.g., "glibc 2.3.4").
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31       _CS_GNU_LIBPTHREAD_VERSION (GNU C library only; since glibc 2.3.2)
32              A  string  which identifies the POSIX implementation supplied by
33              this C library (e.g., "NPTL 2.3.4" or "linuxthreads-0.10").
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35       _CS_PATH
36              A value for the PATH variable  which  indicates  where  all  the
37              POSIX.2 standard utilities can be found.
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39       If  buf is not NULL and size is not zero, confstr() copies the value of
40       the string to buf truncated to size - 1 bytes if necessary, with a null
41       byte  ('\0')  as terminator.  This can be detected by comparing the re‐
42       turn value of confstr() against size.
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44       If size is zero and buf is NULL, confstr() just returns  the  value  as
45       defined below.
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RETURN VALUE

48       If name is a valid configuration variable, confstr() returns the number
49       of bytes (including the terminating null byte) that would  be  required
50       to  hold  the entire value of that variable.  This value may be greater
51       than size, which means that the value in buf is truncated.
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53       If name is a valid configuration variable, but that variable  does  not
54       have a value, then confstr() returns 0.  If name does not correspond to
55       a valid configuration variable, confstr() returns 0, and errno  is  set
56       to EINVAL.
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ERRORS

59       EINVAL The value of name is invalid.
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ATTRIBUTES

62       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
63       tributes(7).
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65       ┌────────────────────────────────────────────┬───────────────┬─────────┐
66       │Interface                                   │ Attribute     │ Value   │
67       ├────────────────────────────────────────────┼───────────────┼─────────┤
68       │confstr()                                   │ Thread safety │ MT-Safe │
69       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

72       POSIX.1-2008.
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HISTORY

75       POSIX.1-2001.
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EXAMPLES

78       The following code fragment determines  the  path  where  to  find  the
79       POSIX.2 system utilities:
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81           char *pathbuf;
82           size_t n;
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84           n = confstr(_CS_PATH, NULL, (size_t) 0);
85           pathbuf = malloc(n);
86           if (pathbuf == NULL)
87               abort();
88           confstr(_CS_PATH, pathbuf, n);
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