Quick Help needed on C

Question

I saw a struct declaration in form of

struct name {
uint8_t type:4;
uint8_t length:6;
}

My question is, why insert a colon between the field name and the literal value?

In particular, what's the use of doing 'type:4'?

https://code.sololearn.com/cvqIJ14p1OBu/?ref=app

Answer 1

It's called bit field,

https://en.cppreference.com/w/cpp/language/bit_field