In C, there is no such name as u8; u8 is the name of a user-defined data type (unsigned char) in the C51 language (single-chip computer C language), as if it had a small name for itself; #define unsigned char u8 The same type is also defined as: U8, uchar, uint8, UINT8... Extensions: u16, U16, uint, uint8, UINT16, etc. are macros of type unsigned int. Extended types also have other data types, such as unsigned long