Can someone explain this colon # syntax

Question

I came across a syntax I've never seen before.

typedef struct SomeStruct
{
    unsigned char ip_version :4;
    unsigned char ip_tos;
    unsigned char ip_frag_offset :5;
    unsigned char ip_more_fragment :1;
    unsigned char ip_dont_fragment :1;
    unsigned char ip_reserved_zero :1;
    unsigned char ip_frag_offset1;
    unsigned char ip_ttl;
} SomeHeader;

What is the colon #; for? Is that the same as using the assignment operator? Why use the colon and is there advantages or a reason this is allowed?

Try googling "bit-fields" – Andy Prowl Jul 12 '13 at 19:26 — Andy Prowl, Jul 12 '13 at 19:26

score 1 · Accepted Answer · answered Jul 12 '13 at 19:29

These are bit fields:

It should be noted you could have found this by searching Google for "c struct syntax". For me, the first result was wikipedia, which has a bit field section

Can someone explain this colon # syntax

1 Answers1