man3/confstr.3

   1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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  24 .\"
  25 .\" Modified Sat Jul 24 19:53:02 1993 by Rik Faith (faith@cs.unc.edu)
  26 .\"
  27 .\" FIXME Many more values for 'name' are supported, some of which
  28 .\" are documented under 'info confstr'.
  29 .\" See <bits/confname.h> for the rest.
  30 .\" These should all be added to this page.
  31 .\" See also the POSIX.1-2001 specification of confstr()
  32 .\"
  33 .TH CONFSTR 3  2015-08-08 "GNU" "Linux Programmer's Manual"
  34 .SH NAME
  35 confstr \- get configuration dependent string variables
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <unistd.h>
  39 .PP
  40 .BI "size_t confstr(int " "name" ", char *" buf ", size_t " len );
  41 .fi
  42 .PP
  43 .in -4n
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .in
  47 .PP
  48 .BR confstr ():
  49 _POSIX_C_SOURCE\ >=\ 2 || _XOPEN_SOURCE
  50 .SH DESCRIPTION
  51 .BR confstr ()
  52 gets the value of configuration-dependent string variables.
  53 .PP
  54 The
  55 .I name
  56 argument is the system variable to be queried.
  57 The following variables are supported:
  58 .TP
  59 .BR _CS_GNU_LIBC_VERSION " (GNU C library only; since glibc 2.3.2)"
  60 A string which identifies the GNU C library version on this system
  61 (e.g., "glibc 2.3.4").
  62 .TP
  63 .BR _CS_GNU_LIBPTHREAD_VERSION " (GNU C library only; since glibc 2.3.2)"
  64 A string which identifies the POSIX implementation supplied by this
  65 C library (e.g., "NPTL 2.3.4" or "linuxthreads-0.10").
  66 .TP
  67 .B _CS_PATH
  68 A value for the
  69 .B PATH
  70 variable which indicates where all the POSIX.2 standard utilities can
  71 be found.
  72 .PP
  73 If
  74 .I buf
  75 is not NULL and
  76 .I len
  77 is not zero,
  78 .BR confstr ()
  79 copies the value of the string to
  80 .I buf
  81 truncated to
  82 .I len \- 1
  83 bytes if necessary, with a null byte (\(aq\\0\(aq) as terminator.
  84 This can be detected by comparing the return value of
  85 .BR confstr ()
  86 against
  87 .IR len .
  88 .PP
  89 If
  90 .I len
  91 is zero and
  92 .I buf
  93 is NULL,
  94 .BR confstr ()
  95 just returns the value as defined below.
  96 .SH RETURN VALUE
  97 If
  98 .I name
  99 is a valid configuration variable,
 100 .BR confstr ()
 101 returns the number of bytes (including the terminating null byte)
 102 that would be required to hold the entire value of that variable.
 103 This value may be greater than
 104 .IR len ,
 105 which means that the value in
 106 .I buf
 107 is truncated.
 108 .PP
 109 If
 110 .I name
 111 is a valid configuration variable,
 112 but that variable does not have a value, then
 113 .BR confstr ()
 114 returns 0.
 115 If
 116 .I name
 117 does not correspond to a valid configuration variable,
 118 .BR confstr ()
 119 returns 0, and
 120 .I errno
 121 is set to
 122 .BR EINVAL .
 123 .SH ERRORS
 124 .TP
 125 .B EINVAL
 126 The value of
 127 .I name
 128 is invalid.
 129 .SH ATTRIBUTES
 130 For an explanation of the terms used in this section, see
 131 .BR attributes (7).
 132 .TS
 133 allbox;
 134 lb lb lb
 135 l l l.
 136 Interface       Attribute       Value
 137 T{
 138 .BR confstr ()
 139 T}      Thread safety   MT-Safe
 140 .TE
 141 .SH CONFORMING TO
 142 POSIX.1-2001, POSIX.1-2008.
 143 .SH EXAMPLE
 144 The following code fragment determines the path where to find
 145 the POSIX.2 system utilities:
 146 .br
 147 .PP
 148 .in +4n
 149 .EX
 150 char *pathbuf;
 151 size_t n;
 152
 153 n = confstr(_CS_PATH, NULL, (size_t) 0);
 154 pathbuf = malloc(n);
 155 if (pathbuf == NULL)
 156     abort();
 157 confstr(_CS_PATH, pathbuf, n);
 158 .fi
 159 .in
 160 .SH SEE ALSO
 161 .BR getconf (1),
 162 .BR sh (1),
 163 .BR exec (3),
 164 .BR fpathconf (3),
 165 .BR pathconf (3),
 166 .BR sysconf (3),
 167 .BR system (3)