[SeoxyS]

It's not a common use case, but I've had to do it. Luckily, it's fairly easy:

    int count_multibytes_encountered(char *text, unsigned long len) {
        int count = 0;
        for (int i = 0; i < len; i++) {
            if ((*(text+i) & 0b10000000) == 0b10000000 &&       // check if it's a multi-char byte
                (~*(text+i) & 0b01000000) == 0b01000000) {      // and check that it's not a leading byte
                count++;
            }
        }
        return count;
    }