tempnam - create a name for a temporary file
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
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 used.
P_tmpdir (as defined in
is used when appropriate.
Finally an implementation-defined directory may be used.
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 cause of the
Allocation of storage failed.
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
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
tempnam() uses at most the first five bytes from
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.
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