Section (3) tempnam
tempnam — create a name for a temporary file
||const char *dir,|
|const char *pfx
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:
In case the environment variable
TMPDIRexists and contains the name of an appropriate directory, that is used.
Otherwise, if the
dirargument 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
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 error.
For an explanation of the terms used in this section, see attributes(7).
||Thread safety||MT-Safe env|
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
/tmp (and this is what glibc does).
Because it dynamically allocates memory used to return the
reentrant, and thus thread safe, unlike tmpnam(3).
generates a different string each time it is called, up to
TMP_MAX (defined in
times. If it is called more than
TMP_MAX times, the behavior is
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
The precise meaning of appropriate is undefined; it is unspecified how accessibility of a directory is determined.
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Copyright (c) 1999 Andries Brouwer (aebcwi.nl)
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