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tmpnam(3S) Standard I/O Functions tmpnam(3S)
NAME
tmpnam, tmpnam_r, tempnam - create a name for a temporary
file
SYNOPSIS
#include <stdio.h>
char *tmpnam(char *s);
char *tmpnam_r(char *s);
char *tempnam(const char *dir, const char *pfx);
MT-LEVEL
See the NOTES section of this page.
DESCRIPTION
These functions generate file names that can safely be used
for a temporary file.
tmpnam() always generates a file name using the path-prefix
defined as P_tmpdir in the <stdio.h> header. 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.
tmpnam_r() has the same functionality as tmpnam() except
that if s is a NULL pointer, the function returns NULL.
tempnam() allows the user to control the choice of a direc-
tory. 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
header is used. If that directory is not accessi-
ble, /tmp will be used as a last resort. This entire
sequence can be up-staged by providing an environment vari-
able TMPDIR in the user's environment, whose value is the
name of the desired temporary-file directory.
Many applications prefer their temporary files to have cer-
tain 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(3C) to get space for the constructed
file name, and returns a pointer to this area. Thus, any
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tmpnam(3S) Standard I/O Functions tmpnam(3S)
pointer value returned from tempnam() may serve as an argu-
ment to free(3C) (see malloc(3C)). If tempnam() cannot
return the expected result for any reason - for example,
malloc(3C) 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.
SEE ALSO
creat(2), unlink(2), fopen(3S), free(3C), malloc(3C),
mktemp(3C), tmpfile(3S)
NOTES
The tmpnam_r() interface is as proposed in the POSIX.4a
Draft #6 document, and is subject to change to be compliant
to the standard when it is accepted.
When compiling multi-thread applications, the _REENTRANT
flag must be defined on the compile line. This flag should
only be used in multi-thread applications.
These functions generate a different file name each time
they are called.
Files created using these functions and either fopen(3S) or
creat(2) 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.
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(3C) and the
file names are chosen to render duplication by other means
unlikely.
tempnam() is safe in multi-thread applications. tmpnam() is
unsafe in multi-thread applications, tmpnam_r() should be
used instead.
On Solaris systems, the default value for P_tmpdir is
/var/tmp.
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