Section: Linux Programmer's Manual (3)
Return to Main Contents
tempnam - create a name for a temporary file
char *tempnam(const char *dir, const char *pfx);
Feature Test Macro Requirements for glibc (see
_BSD_SOURCE || _SVID_SOURCE
function returns a pointer to a string that is a valid filename,
and such that a file with this name did not exist when
The filename suffix of the pathname generated will start with
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
In case the environment variable
contains the name of an appropriate directory, that is used.
Otherwise, if the
argument is non-NULL and appropriate, it is used.
(as defined in
is used when appropriate.
Finally an implementation-defined directory may be used.
The string returned by
is allocated using
and hence should be freed by
On success, the
function returns a pointer to a unique temporary filename.
It returns NULL if a unique name cannot be generated, with
set to indicate the cause of the error.
Allocation of storage failed.
SVr4, 4.3BSD, POSIX.1-2001.
generates names that are difficult to guess,
it is nevertheless possible that between the time that
returns a pathname, and the time that the program opens it,
another program might create that pathname using
or create it as a symbolic link.
This can lead to security holes.
To avoid such possibilities, use the
flag to open the pathname.
Or better yet, use
SUSv2 does not mention the use of
glibc will use it only
when the program is not set-user-ID.
On SVr4, the directory used under d) is
(and this is what glibc does).
Because it dynamically allocates memory used to return the pathname,
is reentrant, and thus thread safe, unlike
function generates a different string each time it is called,
If it is called more than
the behavior is implementation defined.
uses at most the first five bytes from
The glibc implementation of
will fail with the error
upon failure to find a unique name.
The precise meaning of "appropriate" is undefined;
it is unspecified how accessibility of a directory is determined.
Never use this function.
This page is part of release 3.54 of the Linux
A description of the project,
and information about reporting bugs,
can be found at
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
This document was created by
using the manual pages.
Time: 22:02:02 GMT, January 22, 2018