tmpnam, tempnam - create a name for a temporary file
char *tmpnam (char *s);
char *tempnam (const char *dir, const char *pfx);
These functions generate file names that can safely be used for a
tmpnam always generates a file name using the path-prefix defined as
P_tmpdir in the <stdio.h> header file. If s is NULL, tmpnam leaves its
result in an internal static area and returns a pointer to that area.
The next call to tmpnam will destroy the contents of the area. If s is
not NULL, it is assumed to be the address of an array of at least
L_tmpnam bytes, where L_tmpnam is a constant defined in <stdio.h>; tmpnam
places its result in that array and returns s.
tempnam allows the user to control the choice of a directory. The
argument dir points to the name of the directory in which the file is to
be created. If dir is NULL or points to a string that is not a name for
an appropriate directory, the path-prefix defined as P_tmpdir in the
<stdio.h> header file is used. If that directory is not accessible, /tmp
will be used as a last resort. To override this entire sequence, provide
a TMPDIR environment variable in the user's environment; the variable's
value is the name of the desired temporary-file directory. If the
directory specified by the variable TMPDIR is not accessible, the
sequence is then used to determine the temporary-file directory.
Many applications prefer their temporary files to have certain favorite
initial letter sequences in their names. Use the pfx argument for this.
This argument may be NULL or point to a string of up to five characters
to be used as the first few characters of the temporary-file name.
tempnam uses malloc to get space for the constructed file name, and
returns a pointer to this area. Thus, any pointer value returned from
tempnam may serve as an argument to free [see malloc(3C)]. If tempnam
cannot return the expected result for any reason-e.g., malloc failed-or
none of the above mentioned attempts to find an appropriate directory was
successful, a NULL pointer will be returned.
tempnam fails if there is not enough space.
creat(2), unlink(2), fopen(3S), malloc(3C), mktemp(3C), tmpfile(3S).
tmpnam should not be called with s equal to a NULL pointer in a
multithreaded application due to the use of an internal static buffer for
the return value.
These functions generate a different file name each time they are called.
Files created using these functions and either fopen or creat are
temporary only in the sense that they reside in a directory intended for
temporary use, and their names are unique. It is the user's
responsibility to remove the file when its use is ended.
Each call to tmpnam will make 26 attempts to create a filename which does
not duplicate an existing file. If this fails, the first character of s
will be zeroed, and tmpnam will return the empty string.
A call to tempnam will also make 26 attempts to create a filename which
does not duplicate an existing file. If this fails, tempnam will return
If called more than TMP_MAX (defined in stdio.h) times in a single
process, these functions start recycling previously used names.
Between the time a file name is created and the file is opened, it is
possible for some other process to create a file with the same name.
This can never happen if that other process is using these functions or
mktemp and the file names are chosen to render duplication by other means
Both tempnam and tmpname use mktemp(3C). To avoid the possibility of
generating identical filenames via two mechanisms, you should not call
mktemp directly when using tempnam or tmpname unless you can avoid the
use of the filename templates used by these routines.
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