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ctypedefbit-fields

Typedef a bitfield variable

I want to have a typedef that is 1-bit integer, so I though of this typedef int:1 FLAG; but I'm getting errors with it, is there a way I can do so? Thanks

Solution

  • No.

    The smallest addressable "thing" in a C Program is a byte or char.
    A char is at least 8 bits long.
    So you cannot have a type (or objects of any type) with less than 8 bits.

    What you can do is have a type for which objects occupy at least as many bits as a char and ignore most of the bits

    #include <limits.h>
#include <stdio.h>

struct OneBit {
    unsigned int value:1;
};
typedef struct OneBit onebit;

int main(void) {
    onebit x;
    x.value = 1;
    x.value++;
    printf("1 incremented is %u\n", x.value);
    printf("each object of type 'onebit' needs %d bytes (%d bits)\n",
          (int)sizeof x, CHAR_BIT * (int)sizeof x);
    return 0;
}

    You can see the code above running at ideone.