15  Passing a NULL Pointer to _storc() or _storclen()
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     Passing a NULL pointer to _storc() or _storclen() has a special
     meaning: it means you wish to create a true duplicate copy of the
     parameter's current value.  If the specified parameter or array
     element is a character value, a new (duplicate) copy of the data is
     created and stored.  This allows you to modify a string in place
     without locking two copies of it.  Note that, for _storclen(), the
     existing data is duplicated to the extent possible within the
     specified length.  If the specified length is longer than the
     existing value, the excess bytes in the copy are uninitialized.  If
     the existing value is not character type, the new string is left
     uninitialized.  For example:

     .  Storing a new string into an array element:

        char far *p;

        /* create new string in first element of third param */
        _storclen(NULL, 10, 3, 1);

        /* get a locked pointer to the new string */
        p = _parc(3, 1);

        /* put some bytes in the new string */
        strcpy(p, "some bytes");

     .  Modifying an array element in place:

        char far *p;

        /* first dupe the element, expanding the length if needed */
        _storclen(NULL, 100, 3, 1);

        /* get a locked pointer to the copy */
        p = _parc(3, 1);

        /* modify the string */
        strcpy(p + 50, "YOW!");