The WSpanSize method

This method returns the number of characters in the longest initial substring of the wide character string s1 that consists entirely of characters from the wide character string s2.

int WSpanSize(const ITWChar *s1, const ITWChar *s2,
            int nwchars1 = ITLocale::ScanToNul, 
            int nwchars2 = ITLocale::ScanToNul) const

The nwchars1 and nwchars2 parameters specify the length of the s1 and s2 strings. You can provide an integer to specify the number of characters in the corresponding string. Or you can use the constant ITLocale::ScanToNul (the default) to specify that the corresponding string is null-terminated.

If there is an error, this method returns -1. Call ITLocale::GetError() to retrieve a specific error message.