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     The tmpnam function generates a temporary file name that can be
     used to open a temporary file without overwriting an existing
     file. This name is stored in <string>. If <string> is NULL, tmpnam
     leaves the result in an internal static buffer. Thus, any
     subsequent calls destroy this value. If <string> is not NULL, it
     is assumed to point to an array of at least L_tmpnam bytes. (The
     value of L_tmpnam is defined in the STDIO.H include file.) The
     function generates unique file names for up to TMP_MAX calls.
 
     The character string that tmpnam creates consists of the path
     prefix defined by the P_tmpdir entry in STDIO.H, followed by a
     sequence consisting of the digit characters '0' through '9'. The
     numerical value of this string can range from 1 to 65,535.
     Changing the definition of L_tmpnam or P_tmpdir in STDIO.H does
     not change the operation of tmpnam.
 
     The tempnam function allows the program to create a temporary file
     for use in another directory. This file name will be different
     from that of any existing file. The <prefix> argument is the
     prefix to the file name. The tempnam function uses malloc to
     allocate space for the file name; the program is responsible for
     freeing this space when it is no longer needed.
 
     The tempnam function looks for the file with the given name in the
     following directories, listed in order of precedence:
 
     Directory Used                 Conditions
 
     Directory specified by TMP     TMP environment variable is set,
                                    and directory specified by TMP
                                    exists.
 
     dir argument to tempnam        TMP environment variable is not
                                    set, or directory specified by
                                    TMP does not exist.
 
     P_tmpdir in STDIO.H            The <dir> argument is NULL, or
                                    <dir> is name of nonexistent
                                    directory.
 
     Current working directory      P_tmpdir does not exist.
 
     If the search through the locations listed above fails, tempnam
     returns the value NULL.
 
     Return Value
 
     The tmpnam and tempnam functions both return a pointer to the name
     generated, unless it is impossible to create this name or the name
     is not unique. If the name cannot be created or if it already
     exists, tmpnam and tempnam return the value NULL.
                                    -♦-