rent, FILE *fp, int errorcode, const char *argval, const char *progname)
    {
    <I>/* for convenience */</I>
    const char *shortopts = parent-&gt;hdr.shortopts;
    const char *longopts  = parent-&gt;hdr.longopts;
    const char *datatype  = parent-&gt;hdr.datatype;

    /* make argval NULL safe */
    <I>argval = argval ? argval : &quot;&quot;;</I>

    <I>/* prefix all error messages with the program name */</I>
    fprintf(fp,&quot;%s: &quot;,progname);

    switch(errorcode)
        {
        case 