.\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
.\"
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
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.\" 2003-11-15, aeb, added tmpnam_r
.\"
.TH TMPNAM 3  2003-11-15 "" "Linux Programmer's Manual"
.SH NAME
tmpnam, tmpnam_r \- create a name for a temporary file
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.sp
.BI "char *tmpnam(char *" s );
.fi
.SH DESCRIPTION
The
.BR tmpnam ()
function returns a pointer to a string that is a valid filename,
and such that a file with this name did not exist at some point
in time, so that naive programmers may think it
a suitable name for a temporary file.
If the argument
.I s
is NULL this name is generated in an internal static buffer
and may be overwritten by the next call to
.BR tmpnam ().
If
.I s
is not NULL, the name is copied to the character array (of length
at least
.IR L_tmpnam )
pointed to by
.I s
and the value
.I s
is returned in case of success.
.LP
The pathname that is created, has a directory prefix
.IR P_tmpdir .
(Both
.I L_tmpnam
and
.I P_tmpdir
are defined in
.IR <stdio.h> ,
just like the
.B TMP_MAX
mentioned below.)
.SH "RETURN VALUE"
The
.BR tmpnam ()
function returns a pointer to a unique temporary
filename, or NULL if a unique name cannot be generated.
.SH ERRORS
No errors are defined.
.SH "CONFORMING TO"
SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
.SH NOTES
The
.BR tmpnam ()
function generates a different string each time it is called,
up to
.B TMP_MAX
times.
If it is called more than
.B TMP_MAX
times,
the behavior is implementation defined.
.LP
Although
.BR tmpnam ()
generates names that are difficult to guess,
it is nevertheless possible that between the time that
.BR tmpnam ()
returns a pathname, and the time that the program opens it,
another program might create that pathname using
.BR open (2),
or create it as a symbolic link.
This can lead to security holes.
To avoid such possibilities, use the
.BR open (2)
.B O_EXCL
flag to open the pathname.
Or better yet, use
.BR mkstemp (3)
or
.BR tmpfile (3).
.LP
Portable applications that use threads cannot call
.BR tmpnam ()
with NULL parameter if either
.B _POSIX_THREADS
or
.B _POSIX_THREAD_SAFE_FUNCTIONS
is defined.
.LP
A POSIX draft proposed to use a function
.BR tmpnam_r ()
defined by
.sp
.nf
.in +5
char *
tmpnam_r(char *s)
{
    return s ? tmpnam(s) : NULL;
}
.in
.fi
.sp
apparently as a warning not to use NULL.
A few systems implement it.
To get a glibc prototype for this function,
define
.B _SVID_SOURCE
or
.B _BSD_SOURCE
before including
.IR <stdio.h> .
.SH BUGS
Never use this function.
Use
.BR mkstemp (3)
or
.BR tmpfile (3)
instead.
.SH "SEE ALSO"
.BR mkstemp (3),
.BR mktemp (3),
.BR tempnam (3),
.BR tmpfile (3)