man3/confstr.3

   1 .\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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  23 .\" Modified Sat Jul 24 19:53:02 1993 by Rik Faith (faith@cs.unc.edu)
  24 .\" FIXME Many more values for 'name' are supported, some of which
  25 .\"     are documented under 'info confstr'.
  26 .\"     See <bits/confname.h> for the rest.
  27 .\"     These should all be added to this page.
  28 .\"     See also the POSIX.1-2001 specification of confstr()
  29 .TH CONFSTR 3  1993-04-17 "GNU" "Linux Programmer's Manual"
  30 .SH NAME
  31 confstr \- get configuration dependent string variables
  32 .SH SYNOPSIS
  33 .nf
  34 .B #define _POSIX_C_SOURCE 2
  35 or
  36 .B #define _XOPEN_SOURCE
  37 .br
  38 .B #include <unistd.h>
  39 .sp
  40 .BI "size_t confstr(int " "name" ", char *" buf ", size_t " len );
  41 .fi
  42 .SH DESCRIPTION
  43 .BR confstr ()
  44 gets the value of configuration-dependent string variables.
  45 .PP
  46 The
  47 .I name
  48 argument is the system variable to be queried.
  49 The following variables are supported:
  50 .TP
  51 .BR _CS_GNU_LIBC_VERSION " (GNU C library only; since glibc 2.3.2)"
  52 A string which identifies the GNU C library version on this system
  53 (e.g, "glibc 2.3.4").
  54 .TP
  55 .BR _CS_GNU_LIBPTHREAD_VERSION " (GNU C library only; since glibc 2.3.2)"
  56 A string which identifies the POSIX implementation supplied by this
  57 C library (e.g, "NPTL 2.3.4" or "linuxthreads-0.10").
  58 .TP
  59 .B _CS_PATH
  60 A value for the
  61 .B PATH
  62 variable which indicates where all the POSIX.2 standard utilities can
  63 be found.
  64 .PP
  65 If
  66 .I buf
  67 is not NULL and
  68 .I len
  69 is not zero,
  70 .BR confstr ()
  71 copies the value of the string to
  72 .I buf
  73 truncated to
  74 .I len \- 1
  75 characters if necessary, with a null byte ('\\0') as terminator.
  76 This can be detected by comparing the return value of
  77 .BR confstr ()
  78 against
  79 .IR len .
  80 .PP
  81 If
  82 .I len
  83 is zero and
  84 .I buf
  85 is NULL,
  86 .BR confstr ()
  87 just returns the value as defined below.
  88 .SH "RETURN VALUE"
  89 If
  90 .I name
  91 is a valid configuration variable,
  92 .BR confstr ()
  93 returns the number of bytes (including the terminating null byte)
  94 that would be required to hold the entire value of that variable.
  95 This value may be greater than
  96 .IR len ,
  97 which means that the value in
  98 .I buf
  99 is truncated.
 100
 101 If
 102 .I name
 103 is a valid configuration variable,
 104 but that variable does not have a value, then
 105 .BR confstr ()
 106 returns 0.
 107 If
 108 .I name
 109 does not correspond to a valid configuration variable,
 110 .BR confstr ()
 111 returns 0, and
 112 .I errno
 113 is set to
 114 .BR EINVAL .
 115 .SH ERRORS
 116 .TP
 117 .BR EINVAL
 118 If the value of
 119 .I name
 120 is invalid.
 121 .SH EXAMPLE
 122 The following code fragment determines the path where to find
 123 the POSIX.2 system utilities:
 124 .br
 125 .nf
 126 .in 10
 127
 128 char *pathbuf; size_t n;
 129
 130 n = confstr(_CS_PATH,NULL,(size_t)0);
 131 if ((pathbuf = malloc(n)) == NULL) abort();
 132 confstr(_CS_PATH, pathbuf, n);
 133 .SH "CONFORMING TO"
 134 POSIX.1-2001
 135 .SH "SEE ALSO"
 136 .BR sh (1),
 137 .BR exec (3),
 138 .BR system (3),
 139 .BR feature_test_macros (7)