The mktemp() function generates a unique temporary file name from
template. The last six characters of template must be XXXXXX and
these are replaced with a string that makes the filename unique. Since it will
be modified, template must not be a string constant, but should be
declared as a character array.
The mktemp() function returns NULL on error (template did not end
in XXXXXX) and template otherwise. If the call was successful, the last
six bytes of template will have been modified in such a way that the
resulting name is unique (does not exist already). If the call was
unsuccessful, template is made an empty string.
Never use mktemp(). Some implementations follow BSD 4.3 and replace
XXXXXX by the current process id and a single letter, so that at most 26
different names can be returned. Since on the one hand the names are easy to
guess, and on the other hand there is a race between testing whether the name
exists and opening the file, every use of mktemp() is a security risk.
The race is avoided by mkstemp(3).