man3/mktemp.3

   1 .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sat Jul 24 18:48:06 1993 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified Fri Jun 23 01:26:34 1995 by Andries Brouwer (aeb@cwi.nl)
  31 .\" (prompted by Scott Burkett <scottb@IntNet.net>)
  32 .\" Modified Sun Mar 28 23:44:38 1999 by Andries Brouwer (aeb@cwi.nl)
  33 .\"
  34 .TH MKTEMP 3  2017-09-15 "GNU" "Linux Programmer's Manual"
  35 .SH NAME
  36 mktemp \- make a unique temporary filename
  37 .SH SYNOPSIS
  38 .nf
  39 .B #include <stdlib.h>
  40 .PP
  41 .BI "char *mktemp(char *" template );
  42 .fi
  43 .PP
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .PP
  49 .BR mktemp ():
  50 .ad l
  51 .PD 0
  52 .RS 4
  53 .TP 4
  54 Since glibc 2.12:
  55 (_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200112L)
  56     || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  57     || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  58 .TP
  59 Before glibc 2.12:
  60 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500
  61 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  62 .RE
  63 .PD
  64 .ad b
  65 .SH DESCRIPTION
  66 .IR "Never use this function" ;
  67 see BUGS.
  68 .PP
  69 The
  70 .BR mktemp ()
  71 function generates a unique temporary filename
  72 from \fItemplate\fP.
  73 The last six characters of \fItemplate\fP must
  74 be XXXXXX and these are replaced with a string that makes the
  75 filename unique.
  76 Since it will be modified,
  77 .I template
  78 must not be a string constant, but should be declared as a character array.
  79 .SH RETURN VALUE
  80 The
  81 .BR mktemp ()
  82 function always returns \fItemplate\fP.
  83 If a unique name was created, the last six bytes of \fItemplate\fP will
  84 have been modified in such a way that the resulting name is unique
  85 (i.e., does not exist already)
  86 If a unique name could not be created,
  87 \fItemplate\fP is made an empty string, and
  88 .I errno
  89 is set to indicate the error.
  90 .SH ERRORS
  91 .TP
  92 .B EINVAL
  93 The last six characters of \fItemplate\fP were not XXXXXX.
  94 .SH ATTRIBUTES
  95 For an explanation of the terms used in this section, see
  96 .BR attributes (7).
  97 .TS
  98 allbox;
  99 lb lb lb
 100 l l l.
 101 Interface       Attribute       Value
 102 T{
 103 .BR mktemp ()
 104 T}      Thread safety   MT-Safe
 105 .TE
 106 .SH CONFORMING TO
 107 4.3BSD, POSIX.1-2001.
 108 POSIX.1-2008 removes the specification of
 109 .BR mktemp ().
 110 .\" .SH NOTES
 111 .\" The prototype is in
 112 .\" .I <unistd.h>
 113 .\" for libc4, libc5, glibc1; glibc2 follows the Single UNIX Specification
 114 .\" and has the prototype in
 115 .\" .IR <stdlib.h> .
 116 .SH BUGS
 117 Never use
 118 .BR mktemp ().
 119 Some implementations follow 4.3BSD
 120 and replace XXXXXX by the current process ID and a single letter,
 121 so that at most 26 different names can be returned.
 122 Since on the one hand the names are easy to guess, and on the other
 123 hand there is a race between testing whether the name exists and
 124 opening the file, every use of
 125 .BR mktemp ()
 126 is a security risk.
 127 The race is avoided by
 128 .BR mkstemp (3)
 129 and
 130 .BR mkdtemp (3).
 131 .SH SEE ALSO
 132 .BR mktemp (1),
 133 .BR mkdtemp (3),
 134 .BR mkstemp (3),
 135 .BR tempnam (3),
 136 .BR tmpfile (3),
 137 .BR tmpnam (3)