man3/tmpnam.3

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  25 .\" 2003-11-15, aeb, added tmpnam_r
  26 .\"
  27 .TH TMPNAM 3  2015-03-02 "" "Linux Programmer's Manual"
  28 .SH NAME
  29 tmpnam, tmpnam_r \- create a name for a temporary file
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <stdio.h>
  33 .sp
  34 .BI "char *tmpnam(char *" s );
  35 .fi
  36 .SH DESCRIPTION
  37 .B Note:
  38 Avoid use of
  39 .BR tmpnam ();
  40 use
  41 .BR mkstemp (3)
  42 or
  43 .BR tmpfile (3)
  44 instead.
  45
  46 The
  47 .BR tmpnam ()
  48 function returns a pointer to a string that is a valid filename,
  49 and such that a file with this name did not exist at some point
  50 in time, so that naive programmers may think it
  51 a suitable name for a temporary file.
  52 If the argument
  53 .I s
  54 is NULL, this name is generated in an internal static buffer
  55 and may be overwritten by the next call to
  56 .BR tmpnam ().
  57 If
  58 .I s
  59 is not NULL, the name is copied to the character array (of length
  60 at least
  61 .IR L_tmpnam )
  62 pointed to by
  63 .I s
  64 and the value
  65 .I s
  66 is returned in case of success.
  67 .LP
  68 The pathname that is created, has a directory prefix
  69 .IR P_tmpdir .
  70 (Both
  71 .I L_tmpnam
  72 and
  73 .I P_tmpdir
  74 are defined in
  75 .IR <stdio.h> ,
  76 just like the
  77 .B TMP_MAX
  78 mentioned below.)
  79 .SH RETURN VALUE
  80 The
  81 .BR tmpnam ()
  82 function returns a pointer to a unique temporary
  83 filename, or NULL if a unique name cannot be generated.
  84 .SH ERRORS
  85 No errors are defined.
  86 .SH ATTRIBUTES
  87 For an explanation of the terms used in this section, see
  88 .BR attributes (7).
  89 .TS
  90 allbox;
  91 lb lb lb
  92 l l l.
  93 Interface       Attribute       Value
  94 T{
  95 .BR tmpnam ()
  96 T}      Thread safety   MT-Unsafe race:tmpnam/!s
  97 T{
  98 .BR tmpnam_r ()
  99 T}      Thread safety   MT-Safe
 100 .TE
 101 .SH CONFORMING TO
 102 SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
 103 POSIX.1-2008 marks
 104 .BR tmpnam ()
 105 as obsolete.
 106 .SH NOTES
 107 The
 108 .BR tmpnam ()
 109 function generates a different string each time it is called,
 110 up to
 111 .B TMP_MAX
 112 times.
 113 If it is called more than
 114 .B TMP_MAX
 115 times,
 116 the behavior is implementation defined.
 117 .LP
 118 Although
 119 .BR tmpnam ()
 120 generates names that are difficult to guess,
 121 it is nevertheless possible that between the time that
 122 .BR tmpnam ()
 123 returns a pathname, and the time that the program opens it,
 124 another program might create that pathname using
 125 .BR open (2),
 126 or create it as a symbolic link.
 127 This can lead to security holes.
 128 To avoid such possibilities, use the
 129 .BR open (2)
 130 .B O_EXCL
 131 flag to open the pathname.
 132 Or better yet, use
 133 .BR mkstemp (3)
 134 or
 135 .BR tmpfile (3).
 136 .LP
 137 Portable applications that use threads cannot call
 138 .BR tmpnam ()
 139 with a NULL argument if either
 140 .B _POSIX_THREADS
 141 or
 142 .B _POSIX_THREAD_SAFE_FUNCTIONS
 143 is defined.
 144 .LP
 145 A POSIX draft proposed to use a function
 146 .BR tmpnam_r ()
 147 defined by
 148 .sp
 149 .nf
 150 .in +4n
 151 char *
 152 tmpnam_r(char *s)
 153 {
 154     return s ? tmpnam(s) : NULL;
 155 }
 156 .in
 157 .fi
 158 .sp
 159 apparently as a warning not to use NULL.
 160 A few systems implement it.
 161 To get a glibc prototype for this function from
 162 .IR <stdio.h> ,
 163 define
 164 .B _SVID_SOURCE
 165 or
 166 .B _BSD_SOURCE
 167 (before including
 168 .I any
 169 header file).
 170 .SH BUGS
 171 Never use this function.
 172 Use
 173 .BR mkstemp (3)
 174 or
 175 .BR tmpfile (3)
 176 instead.
 177 .SH SEE ALSO
 178 .BR mkstemp (3),
 179 .BR mktemp (3),
 180 .BR tempnam (3),
 181 .BR tmpfile (3)