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.\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.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
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH TEMPNAM 3 2008-08-06 "" "Linux Programmer's Manual"
.SH NAME
tempnam \- create a name for a temporary file
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.sp
.BI "char *tempnam(const char *" dir ", const char *" pfx );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR tempnam ():
_BSD_SOURCE || _SVID_SOURCE
.SH DESCRIPTION
The
.BR tempnam ()
function returns a pointer to a string that is a valid filename,
and such that a file with this name did not exist when
.BR tempnam ()
checked.
The filename suffix of the pathname generated will start with
.I pfx
in case
.I pfx
is a non-NULL string of at most five bytes.
The directory prefix part of the pathname generated is required to
be "appropriate" (often that at least implies writable).
Attempts to find an appropriate directory go through the following
steps:
.TP 3
a)
In case the environment variable
.B TMPDIR
exists and
contains the name of an appropriate directory, that is used.
.TP
b)
Otherwise, if the
.I dir
argument is non-NULL and appropriate, it is used.
.TP
c)
Otherwise,
.I P_tmpdir
(as defined in
.IR <stdio.h> )
is used when appropriate.
.TP
d)
Finally an implementation-defined directory may be used.
.PP
The string returned by
.BR tempnam ()
is allocated using
.BR malloc (3)
and hence should be freed by
.BR free (3).
.SH "RETURN VALUE"
The
.BR tempnam ()
function returns a pointer to a unique temporary
filename, or NULL if a unique name cannot be generated.
.SH ERRORS
.TP
.B ENOMEM
Allocation of storage failed.
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001.
POSIX.1-2008 marks
.BR tempnam ()
as obsolete.
.SH NOTES
Although
.BR tempnam ()
generates names that are difficult to guess,
it is nevertheless possible that between the time that
.BR tempnam ()
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).
SUSv2 does not mention the use of
.BR TMPDIR ;
glibc will use it only
when the program is not set-user-ID.
On SVr4, the directory used under \fBd)\fP is
.I /tmp
(and this is what glibc does).
.LP
Because it dynamically allocates memory used to return the pathname,
.BR tempnam ()
is reentrant, and thus thread safe, unlike
.BR tmpnam (3).
.LP
The
.BR tempnam ()
function generates a different string each time it is called,
up to
.B TMP_MAX
(defined in
.IR <stdio.h> )
times.
If it is called more than
.B TMP_MAX
times,
the behavior is implementation defined.
.LP
.BR tempnam ()
uses at most the first five bytes from
.IR pfx .
The glibc implementation of
.BR tempnam ()
will fail with the error
.B EEXIST
upon failure to find a unique name.
.SH BUGS
The precise meaning of "appropriate" is undefined;
it is unspecified how accessibility of a directory is determined.
Never use this function.
Use
.BR mkstemp (3)
or
.BR tmpfile (3)
instead.
.SH "SEE ALSO"
.BR mkstemp (3),
.BR mktemp (3),
.BR tmpfile (3),
.BR tmpnam (3)
.SH COLOPHON
This page is part of release 3.44 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
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