tempnam - create a name for a temporary file
char *tempnam(const char *dir, const char *pfx);
Feature Test Macro Requirements for glibc (see feature_test_macros
Since glibc 2.19:
Glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
Never use this function.
(3) or tmpfile
() function returns a pointer to a string that is a valid
filename, and such that a file with this name did not exist when
() 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:
- In case the environment variable TMPDIR exists and contains the
name of an appropriate directory, that is used.
- Otherwise, if the dir argument is non-NULL and appropriate, it is
- Otherwise, P_tmpdir (as defined in <stdio.h>) is used
- Finally an implementation-defined directory may be used.
The string returned by tempnam
() is allocated using malloc
hence should be freed by free
On success, the tempnam
() 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.
For an explanation of the terms used in this section, see attributes
SVr4, 4.3BSD, POSIX.1-2001. POSIX.1-2008 marks tempnam
() as obsolete.
() 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
flag to open the pathname. Or better yet, use mkstemp
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)
(and this is what glibc does).
Because it dynamically allocates memory used to return the pathname,
() is reentrant, and thus thread safe, unlike tmpnam
() 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
() 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.