MKTEMP(3)

NAME
mktemp - make temporary file name (unique)

SYNOPSIS
#include <unistd.h>

char * mktemp (char *template);
int mkstemp (char *template);

DESCRIPTION
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.

RETURN VALUES
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.

ERRORS
The mktemp and mkstemp functions may set errno to one of the following values:

    ENOTDIR
        The pathname portion of the template is not an existing directory.

The mktemp and mkstemp functions may also set errno to any value specified by the stat(2) function.

The mkstemp function may also set errno to any value specified by the open(2) function.

NOTES
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 compilers were common. For example, calling mkstemp with an argument of /tmp/tempfile.XXXXXX will result in a core dump due to mkstemp attempting 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.

SEE ALSO
chmod(2), getpid(2), open(2), stat(2)

HISTORY
A mktemp function appeared in Version 7 AT&T UNIX.