What does ':' mean in struct field declarations?

Asked Mar 22 '20 at 15:16

Active Mar 22 '20 at 15:23

Viewed 64 times

Today, I saw an example in this website which was new to me. The provided example is as follow:

struct S {
    char a;     // memory location #1
    int b : 5;  // memory location #2
    int c : 11, // memory location #2 (continued)
          : 0,
        d : 8;  // memory location #3
    struct {
        int ee : 8; // memory location #4
    } e;
} obj; // The object 'obj' consists of 4 separate memory locations

I'm a little bit confused about the ':' in this example, what does "int b : 5;" mean in this example?

edited Mar 22 '20 at 15:23

Al.G.

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asked Mar 22 '20 at 15:16

Hamed Norouzi

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https://en.cppreference.com/w/cpp/language/bit_field – Hans Passant Mar 22 '20 at 15:18
This is a feature you will likely very rarely use. – drescherjm Mar 22 '20 at 15:18
Exactly, I'd never seen anybody use that before. – Hamed Norouzi Mar 22 '20 at 15:21
Not a duplicate but related: [https://stackoverflow.com/questions/4240974/when-is-it-worthwhile-to-use-bit-fields](https://stackoverflow.com/questions/4240974/when-is-it-worthwhile-to-use-bit-fields) – drescherjm Mar 22 '20 at 15:25

What does ':' mean in struct field declarations?

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