man3/tempnam.3

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  25 .TH TEMPNAM 3  2008-08-06 "" "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 .sp
  32 .BI "char *tempnam(const char *" dir ", const char *" pfx );
  33 .fi
  34 .sp
  35 .in -4n
  36 Feature Test Macro Requirements for glibc (see
  37 .BR feature_test_macros (7)):
  38 .in
  39 .sp
  40 .BR tempnam ():
  41 _BSD_SOURCE || _SVID_SOURCE
  42 .SH DESCRIPTION
  43 The
  44 .BR tempnam ()
  45 function returns a pointer to a string that is a valid filename,
  46 and such that a file with this name did not exist when
  47 .BR tempnam ()
  48 checked.
  49 The filename suffix of the pathname generated will start with
  50 .I pfx
  51 in case
  52 .I pfx
  53 is a non-NULL string of at most five bytes.
  54 The directory prefix part of the pathname generated is required to
  55 be "appropriate" (often that at least implies writable).
  56
  57 Attempts to find an appropriate directory go through the following
  58 steps:
  59 .TP 3
  60 a)
  61 In case the environment variable
  62 .B TMPDIR
  63 exists and
  64 contains the name of an appropriate directory, that is used.
  65 .TP
  66 b)
  67 Otherwise, if the
  68 .I dir
  69 argument is non-NULL and appropriate, it is used.
  70 .TP
  71 c)
  72 Otherwise,
  73 .I P_tmpdir
  74 (as defined in
  75 .IR <stdio.h> )
  76 is used when appropriate.
  77 .TP
  78 d)
  79 Finally an implementation-defined directory may be used.
  80 .PP
  81 The string returned by
  82 .BR tempnam ()
  83 is allocated using
  84 .BR malloc (3)
  85 and hence should be freed by
  86 .BR free (3).
  87 .SH RETURN VALUE
  88 The
  89 .BR tempnam ()
  90 function returns a pointer to a unique temporary
  91 filename, or NULL if a unique name cannot be generated.
  92 .SH ERRORS
  93 .TP
  94 .B ENOMEM
  95 Allocation of storage failed.
  96 .SH CONFORMING TO
  97 SVr4, 4.3BSD, POSIX.1-2001.
  98 POSIX.1-2008 marks
  99 .BR tempnam ()
 100 as obsolete.
 101 .SH NOTES
 102 Although
 103 .BR tempnam ()
 104 generates names that are difficult to guess,
 105 it is nevertheless possible that between the time that
 106 .BR tempnam ()
 107 returns a pathname, and the time that the program opens it,
 108 another program might create that pathname using
 109 .BR open (2),
 110 or create it as a symbolic link.
 111 This can lead to security holes.
 112 To avoid such possibilities, use the
 113 .BR open (2)
 114 .B O_EXCL
 115 flag to open the pathname.
 116 Or better yet, use
 117 .BR mkstemp (3)
 118 or
 119 .BR tmpfile (3).
 120
 121 SUSv2 does not mention the use of
 122 .BR TMPDIR ;
 123 glibc will use it only
 124 when the program is not set-user-ID.
 125 On SVr4, the directory used under \fBd)\fP is
 126 .I /tmp
 127 (and this is what glibc does).
 128 .LP
 129 Because it dynamically allocates memory used to return the pathname,
 130 .BR tempnam ()
 131 is reentrant, and thus thread safe, unlike
 132 .BR tmpnam (3).
 133 .LP
 134 The
 135 .BR tempnam ()
 136 function generates a different string each time it is called,
 137 up to
 138 .B TMP_MAX
 139 (defined in
 140 .IR <stdio.h> )
 141 times.
 142 If it is called more than
 143 .B TMP_MAX
 144 times,
 145 the behavior is implementation defined.
 146 .LP
 147 .BR tempnam ()
 148 uses at most the first five bytes from
 149 .IR pfx .
 150
 151 The glibc implementation of
 152 .BR tempnam ()
 153 will fail with the error
 154 .B EEXIST
 155 upon failure to find a unique name.
 156 .SH BUGS
 157 The precise meaning of "appropriate" is undefined;
 158 it is unspecified how accessibility of a directory is determined.
 159
 160 Never use this function.
 161 Use
 162 .BR mkstemp (3)
 163 or
 164 .BR tmpfile (3)
 165 instead.
 166 .SH SEE ALSO
 167 .BR mkstemp (3),
 168 .BR mktemp (3),
 169 .BR tmpfile (3),
 170 .BR tmpnam (3)