man3/tmpnam.3

   1 '\" t
   2 .\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .\" 2003-11-15, aeb, added tmpnam_r
   7 .\"
   8 .TH tmpnam 3 (date) "Linux man-pages (unreleased)"
   9 .SH NAME
  10 tmpnam, tmpnam_r \- create a name for a temporary file
  11 .SH LIBRARY
  12 Standard C library
  13 .RI ( libc ", " \-lc )
  14 .SH SYNOPSIS
  15 .nf
  16 .B #include <stdio.h>
  17 .PP
  18 .BI "[[deprecated]] char *tmpnam(char *" s );
  19 .BI "[[deprecated]] char *tmpnam_r(char *" s );
  20 .fi
  21 .PP
  22 .RS -4
  23 Feature Test Macro Requirements for glibc (see
  24 .BR feature_test_macros (7)):
  25 .RE
  26 .PP
  27 .BR tmpnam_r ()
  28 .nf
  29     Since glibc 2.19:
  30         _DEFAULT_SOURCE
  31     Up to and including glibc 2.19:
  32         _BSD_SOURCE || _SVID_SOURCE
  33 .fi
  34 .SH DESCRIPTION
  35 .B Note:
  36 avoid using these functions; use
  37 .BR mkstemp (3)
  38 or
  39 .BR tmpfile (3)
  40 instead.
  41 .PP
  42 The
  43 .BR tmpnam ()
  44 function returns a pointer to a string that is a valid filename,
  45 and such that a file with this name did not exist at some point
  46 in time, so that naive programmers may think it
  47 a suitable name for a temporary file.
  48 If the argument
  49 .I s
  50 is NULL, this name is generated in an internal static buffer
  51 and may be overwritten by the next call to
  52 .BR tmpnam ().
  53 If
  54 .I s
  55 is not NULL, the name is copied to the character array (of length
  56 at least
  57 .IR L_tmpnam )
  58 pointed to by
  59 .I s
  60 and the value
  61 .I s
  62 is returned in case of success.
  63 .PP
  64 The created pathname has a directory prefix
  65 .IR P_tmpdir .
  66 (Both
  67 .I L_tmpnam
  68 and
  69 .I P_tmpdir
  70 are defined in
  71 .IR <stdio.h> ,
  72 just like the
  73 .B TMP_MAX
  74 mentioned below.)
  75 .PP
  76 The
  77 .BR tmpnam_r ()
  78 function performs the same task as
  79 .BR tmpnam (),
  80 but returns NULL (to indicate an error) if
  81 .I s
  82 is NULL.
  83 .SH RETURN VALUE
  84 These functions return a pointer to a unique temporary
  85 filename, or NULL if a unique name cannot be generated.
  86 .SH ERRORS
  87 No errors are defined.
  88 .SH ATTRIBUTES
  89 For an explanation of the terms used in this section, see
  90 .BR attributes (7).
  91 .TS
  92 allbox;
  93 lbx lb lb
  94 l l l.
  95 Interface       Attribute       Value
  96 T{
  97 .na
  98 .nh
  99 .BR tmpnam ()
 100 T}      Thread safety   MT-Unsafe race:tmpnam/!s
 101 T{
 102 .na
 103 .nh
 104 .BR tmpnam_r ()
 105 T}      Thread safety   MT-Safe
 106 .TE
 107 .sp 1
 108 .SH STANDARDS
 109 .TP
 110 .BR tmpnam ()
 111 C11, POSIX.1-2008.
 112 .TP
 113 .BR tmpnam_r ()
 114 None.
 115 .SH HISTORY
 116 .TP
 117 .BR tmpnam ()
 118 SVr4, 4.3BSD, C89, POSIX.1-2001.
 119 Obsolete in POSIX.1-2008.
 120 .TP
 121 .BR tmpnam_r ()
 122 Solaris.
 123 .SH NOTES
 124 The
 125 .BR tmpnam ()
 126 function generates a different string each time it is called,
 127 up to
 128 .B TMP_MAX
 129 times.
 130 If it is called more than
 131 .B TMP_MAX
 132 times,
 133 the behavior is implementation defined.
 134 .PP
 135 Although these functions generate names that are difficult to guess,
 136 it is nevertheless possible that between the time that
 137 the pathname is returned and the time that the program opens it,
 138 another program might create that pathname using
 139 .BR open (2),
 140 or create it as a symbolic link.
 141 This can lead to security holes.
 142 To avoid such possibilities, use the
 143 .BR open (2)
 144 .B O_EXCL
 145 flag to open the pathname.
 146 Or better yet, use
 147 .BR mkstemp (3)
 148 or
 149 .BR tmpfile (3).
 150 .PP
 151 Portable applications that use threads cannot call
 152 .BR tmpnam ()
 153 with a NULL argument if either
 154 .B _POSIX_THREADS
 155 or
 156 .B _POSIX_THREAD_SAFE_FUNCTIONS
 157 is defined.
 158 .SH BUGS
 159 Never use these functions.
 160 Use
 161 .BR mkstemp (3)
 162 or
 163 .BR tmpfile (3)
 164 instead.
 165 .SH SEE ALSO
 166 .BR mkstemp (3),
 167 .BR mktemp (3),
 168 .BR tempnam (3),
 169 .BR tmpfile (3)