Returns a character string giving the equivalence string of
    SYS$COMMAND. This is the name of the controlling terminal.

    Format

      #include  <stdio.h>

      char *ctermid  (char *str);

1 - Function Variants

    The ctermid function has variants named _ctermid32 and _ctermid64
    for use with 32-bit and 64-bit pointer sizes, respectively.

2 - Argument

 str

    Must be a pointer to an array of characters. If this argument is
    NULL, the filename is stored internally and might be overwritten
    by the next ctermid call. Otherwise, the filename is stored
    beginning at the location indicated by the argument. The argument
    must point to a storage area of length L_ctermid (defined by the
    <stdio.h> header file).

3 - Return Value

    pointer            Points to a character string.