man3/tempnam.3

   1 .\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
   2 .\"
   3 .\" %%%LICENSE_START(VERBATIM)
   4 .\" Permission is granted to make and distribute verbatim copies of this
   5 .\" manual provided the copyright notice and this permission notice are
   6 .\" preserved on all copies.
   7 .\"
   8 .\" Permission is granted to copy and distribute modified versions of this
   9 .\" manual under the conditions for verbatim copying, provided that the
  10 .\" entire resulting derived work is distributed under the terms of a
  11 .\" permission notice identical to this one.
  12 .\"
  13 .\" Since the Linux kernel and libraries are constantly changing, this
  14 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  15 .\" responsibility for errors or omissions, or for damages resulting from
  16 .\" the use of the information contained herein.  The author(s) may not
  17 .\" have taken the same level of care in the production of this manual,
  18 .\" which is licensed free of charge, as they might when working
  19 .\" professionally.
  20 .\"
  21 .\" Formatted or processed versions of this manual, if unaccompanied by
  22 .\" the source, must acknowledge the copyright and authors of this work.
  23 .\" %%%LICENSE_END
  24 .\"
  25 .TH TEMPNAM 3  2017-09-15 "" "Linux Programmer's Manual"
  26 .SH NAME
  27 tempnam \- create a name for a temporary file
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <stdio.h>
  31 .PP
  32 .BI "char *tempnam(const char *" dir ", const char *" pfx );
  33 .fi
  34 .PP
  35 .in -4n
  36 Feature Test Macro Requirements for glibc (see
  37 .BR feature_test_macros (7)):
  38 .in
  39 .PP
  40 .BR tempnam ():
  41     Since glibc 2.19:
  42         _DEFAULT_SOURCE
  43     Glibc 2.19 and earlier:
  44         _BSD_SOURCE || _SVID_SOURCE
  45 .SH DESCRIPTION
  46 .I "Never use this function."
  47 Use
  48 .BR mkstemp (3)
  49 or
  50 .BR tmpfile (3)
  51 instead.
  52 .PP
  53 The
  54 .BR tempnam ()
  55 function returns a pointer to a string that is a valid filename,
  56 and such that a file with this name did not exist when
  57 .BR tempnam ()
  58 checked.
  59 The filename suffix of the pathname generated will start with
  60 .I pfx
  61 in case
  62 .I pfx
  63 is a non-NULL string of at most five bytes.
  64 The directory prefix part of the pathname generated is required to
  65 be "appropriate" (often that at least implies writable).
  66 .PP
  67 Attempts to find an appropriate directory go through the following
  68 steps:
  69 .TP 3
  70 a)
  71 In case the environment variable
  72 .B TMPDIR
  73 exists and
  74 contains the name of an appropriate directory, that is used.
  75 .TP
  76 b)
  77 Otherwise, if the
  78 .I dir
  79 argument is non-NULL and appropriate, it is used.
  80 .TP
  81 c)
  82 Otherwise,
  83 .I P_tmpdir
  84 (as defined in
  85 .IR <stdio.h> )
  86 is used when appropriate.
  87 .TP
  88 d)
  89 Finally an implementation-defined directory may be used.
  90 .PP
  91 The string returned by
  92 .BR tempnam ()
  93 is allocated using
  94 .BR malloc (3)
  95 and hence should be freed by
  96 .BR free (3).
  97 .SH RETURN VALUE
  98 On success, the
  99 .BR tempnam ()
 100 function returns a pointer to a unique temporary filename.
 101 It returns NULL if a unique name cannot be generated, with
 102 .I errno
 103 set to indicate the cause of the error.
 104 .SH ERRORS
 105 .TP
 106 .B ENOMEM
 107 Allocation of storage failed.
 108 .SH ATTRIBUTES
 109 For an explanation of the terms used in this section, see
 110 .BR attributes (7).
 111 .TS
 112 allbox;
 113 lb lb lb
 114 l l l.
 115 Interface       Attribute       Value
 116 T{
 117 .BR tempnam ()
 118 T}      Thread safety   MT-Safe env
 119 .TE
 120 .SH CONFORMING TO
 121 SVr4, 4.3BSD, POSIX.1-2001.
 122 POSIX.1-2008 marks
 123 .BR tempnam ()
 124 as obsolete.
 125 .SH NOTES
 126 Although
 127 .BR tempnam ()
 128 generates names that are difficult to guess,
 129 it is nevertheless possible that between the time that
 130 .BR tempnam ()
 131 returns a pathname, and the time that the program opens it,
 132 another program might create that pathname using
 133 .BR open (2),
 134 or create it as a symbolic link.
 135 This can lead to security holes.
 136 To avoid such possibilities, use the
 137 .BR open (2)
 138 .B O_EXCL
 139 flag to open the pathname.
 140 Or better yet, use
 141 .BR mkstemp (3)
 142 or
 143 .BR tmpfile (3).
 144 .PP
 145 SUSv2 does not mention the use of
 146 .BR TMPDIR ;
 147 glibc will use it only
 148 when the program is not set-user-ID.
 149 On SVr4, the directory used under \fBd)\fP is
 150 .I /tmp
 151 (and this is what glibc does).
 152 .PP
 153 Because it dynamically allocates memory used to return the pathname,
 154 .BR tempnam ()
 155 is reentrant, and thus thread safe, unlike
 156 .BR tmpnam (3).
 157 .PP
 158 The
 159 .BR tempnam ()
 160 function generates a different string each time it is called,
 161 up to
 162 .B TMP_MAX
 163 (defined in
 164 .IR <stdio.h> )
 165 times.
 166 If it is called more than
 167 .B TMP_MAX
 168 times,
 169 the behavior is implementation defined.
 170 .PP
 171 .BR tempnam ()
 172 uses at most the first five bytes from
 173 .IR pfx .
 174 .PP
 175 The glibc implementation of
 176 .BR tempnam ()
 177 fails with the error
 178 .B EEXIST
 179 upon failure to find a unique name.
 180 .SH BUGS
 181 The precise meaning of "appropriate" is undefined;
 182 it is unspecified how accessibility of a directory is determined.
 183 .SH SEE ALSO
 184 .BR mkstemp (3),
 185 .BR mktemp (3),
 186 .BR tmpfile (3),
 187 .BR tmpnam (3)