tmpnam(3) — Linux manual pages

Linux manual pages	Section 3

Name

tmpnam, tmpnam_r — create a name for a temporary file

Synopsis

        #include <stdio.h>

char *tmpnam( char *s);

DESCRIPTION

	Note
	Avoid use of `tmpnam`(); use mkstemp(3) or tmpfile(3) instead.

The 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 s is NULL, this name is generated in an internal static buffer and may be overwritten by the next call to tmpnam(). If s is not NULL, the name is copied to the character array (of length at least L_tmpnam) pointed to by s and the value s is returned in case of success.

The pathname that is created, has a directory prefix P_tmpdir. (Both L_tmpnam and P_tmpdir are defined in <stdio.h> just like the TMP_MAX mentioned below.)

RETURN VALUE

The tmpnam() function returns a pointer to a unique temporary filename, or NULL if a unique name cannot be generated.

ERRORS

No errors are defined.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
`tmpnam`()	Thread safety	MT-Unsafe race:tmpnam/!s
`tmpnam_r`()	Thread safety	MT-Safe

CONFORMING TO

SVr4, 4.3BSD, C89, C99, POSIX.1-2001. POSIX.1-2008 marks tmpnam() as obsolete.

NOTES

The tmpnam() function generates a different string each time it is called, up to TMP_MAX times. If it is called more than TMP_MAX times, the behavior is implementation defined.

Although tmpnam() generates names that are difficult to guess, it is nevertheless possible that between the time that tmpnam() returns a pathname, and the time that the program opens it, another program might create that pathname using open(2), or create it as a symbolic link. This can lead to security holes. To avoid such possibilities, use the open(2) O_EXCL flag to open the pathname. Or better yet, use mkstemp(3) or tmpfile(3).

Portable applications that use threads cannot call tmpnam() with a NULL argument if either _POSIX_THREADS or _POSIX_THREAD_SAFE_FUNCTIONS is defined.

A POSIX draft proposed to use a function tmpnam_r() defined by

char *
tmpnam_r(char *s)
{
    return s ? tmpnam(s) : NULL;
}

apparently as a warning not to use NULL. A few systems implement it and an implementation is provided in glibc.

BUGS

Never use this function. Use mkstemp(3) or tmpfile(3) instead.

COLOPHON

This page is part of release 4.07 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.

  Copyright (c) 1999 Andries Brouwer (aebcwi.nl)

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2003-11-15, aeb, added tmpnam_r