Returns a pointer to a character string containing the name of
    the user initiating the current process.

    Format

      #include  <unistd.h> (X/Open, POSIX-1)

      #include  <stdio.h> (X/Open)

      char *cuserid  (char *str);

1 - Function Variants

    The cuserid function has variants named _cuserid32 and _cuserid64
    for use with 32-bit and 64-bit pointer sizes, respectively.

2 - Argument

 str

    If this argument is NULL, the user name is stored internally. If
    the argument is not NULL, it points to a storage area of length
    L_cuserid (defined by the <stdio.h> header file), and the name is
    written into that storage. If the user name is a null string, the
    function returns NULL.

3 - Return Values

    pointer            Points to a string.
    NULL               If the user name is a null string.