int mkstemp(char *template); The mkstemp() function shall
replace the contents of the string pointed to by template by a
unique filename, and return a file descriptor for the file open
for reading and writing. The function thus prevents any possible
race condition between testing whether the file exists and
opening it for use. The string in template should look like a
filename with six trailing 'X' s; mkstemp() replaces each 'X'
with a character from the portable filename character set. The
characters are chosen such that the resulting name does not
duplicate the name of an existing file at the time of a call to
mkstemp(). Upon successful completion, mkstemp() shall return an
open file descriptor. Otherwise, -1 shall be returned if no
suitable file could be created. No errors are defined. The
following sections are informative. The following example
creates a file with a 10-character name beginning with the
characters "file" and opens the file for reading and writing.
The value returned as the value of fd is