C struct: what does this mean? [duplicate]

Question

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What does a colon in a struct declaration mean, such as :1, :7, :16, or :32? (3 answers)

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What does 'unsigned temp:3' in a struct or union mean? [duplicate] (4 answers)

Closed 8 years ago.

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

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

Answer 1

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.

Answer 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.