man3/tmpnam.3

.\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
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.\" 2003-11-15, aeb, added tmpnam_r
.\"
.TH TMPNAM 3  2021-03-22 "" "Linux Programmer's Manual"
.SH NAME
tmpnam, tmpnam_r \- create a name for a temporary file
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.PP
.BI "char *tmpnam(char *" s );
.BI "char *tmpnam_r(char *" s );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR tmpnam_r ()
.nf
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Up to and including glibc 2.19:
        _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
.B Note:
avoid using these functions; use
.BR mkstemp (3)
or
.BR tmpfile (3)
instead.
.PP
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.
.PP
The created pathname 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.)
.PP
The
.BR tmpnam_r ()
function performs the same task as
.BR tmpnam (),
but returns NULL (to indicate an error) if
.I s
is NULL.
.SH RETURN VALUE
These functions return a pointer to a unique temporary
filename, or NULL if a unique name cannot be generated.
.SH ERRORS
No errors are defined.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR tmpnam ()
T}	Thread safety	MT-Unsafe race:tmpnam/!s
T{
.BR tmpnam_r ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
.BR tmpnam ():
SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
POSIX.1-2008 marks
.BR tmpnam ()
as obsolete.
.PP
.BR tmpnam_r ()
is a nonstandard extension that is also available
.\" Appears to be on Solaris
on a few other systems.
.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.
.PP
Although these functions generate names that are difficult to guess,
it is nevertheless possible that between the time that
the pathname is returned 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).
.PP
Portable applications that use threads cannot call
.BR tmpnam ()
with a NULL argument if either
.B _POSIX_THREADS
or
.B _POSIX_THREAD_SAFE_FUNCTIONS
is defined.
.SH BUGS
Never use these functions.
Use
.BR mkstemp (3)
or
.BR tmpfile (3)
instead.
.SH SEE ALSO
.BR mkstemp (3),
.BR mktemp (3),
.BR tempnam (3),
.BR tmpfile (3)