tempnam - create a name for a temporary file
Standard C library (
libc,
-lc)
#include <stdio.h>
char *tempnam(const char *dir, const char *pfx);
tempnam():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
Never use this function. Use
mkstemp(3) or
tmpfile(3)
instead.
The
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
tempnam() checked. The filename suffix of the pathname generated will
start with
pfx in case
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:
- a)
- In case the environment variable TMPDIR exists and
contains the name of an appropriate directory, that is used.
- b)
- Otherwise, if the dir argument is non-NULL and
appropriate, it is used.
- c)
- Otherwise, P_tmpdir (as defined in
<stdio.h>) is used when appropriate.
- d)
- Finally an implementation-defined directory may be
used.
The string returned by
tempnam() is allocated using
malloc(3) and
hence should be freed by
free(3).
On success, the
tempnam() function returns a pointer to a unique
temporary filename. It returns NULL if a unique name cannot be generated, with
errno set to indicate the error.
- ENOMEM
- Allocation of storage failed.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
tempnam () |
Thread safety |
MT-Safe env |
SVr4, 4.3BSD, POSIX.1-2001. POSIX.1-2008 marks
tempnam() as obsolete.
Although
tempnam() generates names that are difficult to guess, it is
nevertheless possible that between the time that
tempnam() 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).
SUSv2 does not mention the use of
TMPDIR; glibc will use it only when the
program is not set-user-ID. On SVr4, the directory used under
d) is
/tmp (and this is what glibc does).
Because it dynamically allocates memory used to return the pathname,
tempnam() is reentrant, and thus thread safe, unlike
tmpnam(3).
The
tempnam() function generates a different string each time it is
called, up to
TMP_MAX (defined in
<stdio.h>) times. If it
is called more than
TMP_MAX times, the behavior is implementation
defined.
tempnam() uses at most the first five bytes from
pfx.
The glibc implementation of
tempnam() fails with the error
EEXIST
upon failure to find a unique name.
The precise meaning of "appropriate" is undefined; it is unspecified
how accessibility of a directory is determined.
mkstemp(3),
mktemp(3),
tmpfile(3),
tmpnam(3)