If you're using UTF-8, use either uint8_t* (preferred) or char. If you're using UTF-32, use uint32_t. If you're using UTF-16, don't. As far as library support

If you're using UTF-8, use either uint8_t* (preferred) or char. If you're using UTF-32, use uint32_t. If you're using UTF-16, don't. As far as library support goes, there are a few good Unicode libraries for C, most notably ICU4C.