MKTEMP(3) Library Routines MKTEMP(3)
mktemp - make temporary file name (unique)
char * mktemp (char *template);
int mkstemp (char *template);
The mktemp function takes the given file name template and overwrites a
portion of it to create a file name. This file name is unique and
suitable for use by the application. The template may be any file name
with some number of X?s appended to it, for example /tmp/temp.XXXX.
The trailing X?s are replaced with the current process number and/or a
unique letter combination. The number of unique file names mktemp can
return depends on the number of X?s provided; six X?s will result in
mktemp testing roughly 26 ** 6 combinations.
The mkstemp function makes the same replacement to the template and
creates the template file, mode 0600, returning a file descriptor
opened for reading and writing. This avoids the race between testing
for a file's existence and opening it for use.
The mktemp function returns a pointer to the template on success and
NULL on failure. The mkstemp function returns -1 if no suitable file
could be created. If either call fails an error code is placed in the
global variable errno.
The mktemp and mkstemp functions may set errno to one of the following
The pathname portion of the template is not an existing
The mktemp and mkstemp functions may also set errno to any value speci-
fied by the stat(2) function.
The mkstemp function may also set errno to any value specified by the
A common problem that results in a core dump on many architectures is
that the programmer passes in a read-only string to mktemp or mkstemp.
This is common with programs that were developed before ANSI/C compil-
ers were common. For example, calling mkstemp with an argument of
/tmp/tempfile.XXXXXX will result in a core dump due to mkstemp attempt-
ing to modify the string constant that was given. If the program in
question makes heavy use of that type of function call, some compilers
have the option of compiling the program so that it will store string
constants in a writable segment of memory (in the data rather than the
text segment). While it is good programming practise to avoid this
problem, it is not strictly necessary under GNO due to the lack of a
write-only text segment.
chmod(2), getpid(2), open(2), stat(2)
A mktemp function appeared in Version 7 AT&T UNIX.
GNO 27 January 1997 MKTEMP(3)
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