C struct: what does this mean?

Question

typedef struct{
        unsigned  flanke:1;         
        unsigned  lastState:1;  
        } flanke_t;

I do not understand the ":1". Please help me, thx.

have a look here: http://c-faq.com/struct/bitfield0.html – Najzero Jun 12 '13 at 12:33 — Najzero, Jun 12 '13 at 12:33
":1" means occupies 1 bit, (not the value 1) – David Ranieri Jun 12 '13 at 12:58 — David Ranieri, Jun 12 '13 at 12:58

Stasik · Accepted Answer · 2013-06-12T13:04:58.240

3

These are bit fields: https://en.wikipedia.org/wiki/Bit_field. Here you just reserve 1 bit for 'flanke' and one for the 'lastState'. The type has to be unsigned int.

edited Jun 12 '13 at 13:04

answered Jun 12 '13 at 12:30

Stasik

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+1, but this link have some Microsoft specifics, I suggest https://en.wikipedia.org/wiki/Bit_field – David Ranieri Jun 12 '13 at 12:59

score 2 · Answer 2 · answered Jun 12 '13 at 12:30

2

What you see here is bit field declaration usage. it is used to indicate the number of bits a given structure member will occupy in the structure so its main usage is to pack a structure so that it occupies less memory.

answered Jun 12 '13 at 12:30

Ivaylo Strandjev

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C struct: what does this mean?

2 Answers2