TMPFILE(3)

NAME
tempnam, tmpfile, tmpnam - temporary file routines

SYNOPSIS
#include <stdio.h>
FILE *
tmpfile(void);
char *
tmpnam(char *str);
char *
tempnam(const char *tmpdir, const char *prefix);

DESCRIPTION
The tmpfile() function returns a pointer to a stream associated with a file descriptor returned by the routine mkstemp(3). The created file is unlinked before tmpfile() returns, causing the file to be automatically deleted when the last reference to it is closed. The file is opened with the access value ‘w+’.

The tmpnam() function returns a pointer to a file name, in the P_tmpdir directory, which did not reference an existing file at some indeterminate point in the past. P_tmpdir is defined in the include file <stdio.h>. If the argument s is non-NULL, the file name is copied to the buffer it references. Otherwise, the file name is copied to a static buffer. In either case, tmpnam() returns a pointer to the file name.

The buffer referenced by s is expected to be at least L_tmpnam bytes in length. L_tmpnam is defined in the include file <stdio.h>.

The tempnam() function is similar to tmpnam(), but provides the ability to specify the directory which will contain the temporary file and the file name prefix.

The environment variable TMPDIR (if set), the argument tmpdir (if non-NULL), the directory P_tmpdir, and the directory /tmp are tried, in the listed order, as directories in which to store the temporary file.

The argument prefix, if non-NULL, is used to specify a file name prefix, which will be the first part of the created file name. Tempnam() allocates memory in which to store the file name; the returned pointer may be used as a subsequent argument to free(3).

RETURN VALUES
The tmpfile() function returns a pointer to an open file stream on success, and a NULL pointer on error.

The tmpnam() and tempfile() functions return a pointer to a file name on success, and a NULL pointer on error.

ERRORS
The tmpfile() function may fail and set the global variable errno for any of the errors specified for the library functions fdopen(3) or mkstemp(3).

The tmpnam() function may fail and set errno for any of the errors specified for the library function mktemp(3).

The tempnam() function may fail and set errno for any of the errors specified for the library functions malloc(3) or mktemp(3).

SEE ALSO
mkstemp(3), mktemp(3)

STANDARDS
The tmpfile() and tmpnam() functions conform to ansiC.

BUGS
These interfaces are provided for System V and ANSI compatibility only. The mkstemp(3) interface is strongly preferred.

There are four important problems with these interfaces (as well as with the historic mktemp(3) interface). First, there is an obvious race between file name selection and file creation and deletion. Second, most historic implementations provide only a limited number of possible temporary file names (usually 26) before file names will start being recycled. Third, the System V implementations of these functions (and of mktemp) use the access(2) function to determine whether or not the temporary file may be created. This has obvious ramifications for setuid or setgid programs, complicating the portable use of these interfaces in such programs. Finally, there is no specification of the permissions with which the temporary files are created.

This implementation does not have these flaws, but portable software cannot depend on that. In particular, the tmpfile() interface should not be used in software expected to be used on other systems if there is any possibility that the user does not wish the temporary file to be publicly readable and writable.