C / C++ / MFC

template<class StringType_>
    void basic_regexp<StringType_>::insert_range(
    string_set_type& c_set,         // set to insert range into
    const string_type& s1,          // lower range: single-character string
    const string_type& s2) const    // upper range: single-character string
 {
    // Both character substrings must be the same size (multibyte test)
    if( s1.size() != s2.size() )
        throw_char_range_error();

    // Get possible single-byte lower and upper range characters
    char_type lower = s1[0];
    char_type upper = s2[0];
    char_type leadbyte = 0;

    // Get lead byte if any
    if( s1.size() > 1 )
        leadbyte = lower;

    // If lead byte
    if( leadbyte )
    {
        // Lead bytes must match; since we are trying to avoid
        // spaning non-contiguous sequences.
        if( lower != upper )
            throw_char_range_error();

        // Use trailing bytes as lower and upper range bytes
        lower = s1[1];
        upper = s2[1];
    }

    // Make sure the range is valid
    if( lower > upper )
        throw_char_range_error();

    // Insert range of characters into substring set
    string_type s;
    for( ; lower <= upper; ++lower )
    {
        s.clear();
        if( leadbyte )
        {
            s += leadbyte;
            s += lower;

            // Avoid invalid character sequences
            if( mb_len(s,2) != 2 )
                continue;
        }
        else
        {
            s += lower;
        }
        c_set.insert(s);
    }
}