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0xPIT/gist:7dd7f043dc55a0a097b3

Created October 31, 2014 16:16
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Bit Fields in Gcc: Don't forget to pack!
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gistfile1.txt
#include <stdio.h>
typedef struct bits_packed {
unsigned int b0:1;
unsigned int b1:1;
unsigned int b2:1;
unsigned int b3:1;
unsigned int b4:1;
unsigned int b5:1;
unsigned int b6:1;
unsigned int b7:1;
} __attribute__((packed)) Bits_t;
typedef struct bits_unpacked {
unsigned int b0:1;
unsigned int b1:1;
unsigned int b2:1;
unsigned int b3:1;
unsigned int b4:1;
unsigned int b5:1;
unsigned int b6:1;
unsigned int b7:1;
} Bits_u_t;
int main() {
Bits_t bits;
Bits_u_t bits_u;
printf("bits: %lu, bits_u: %lu\n", sizeof(bits), sizeof(bits_u));
}
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0xPIT commented Oct 31, 2014

gcc test.bit.c && ./a.out
bits: 1, bits_u: 4

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