Setting groups of bits from a structure to a value

Question

Let's say I have this structure:

typedef struct {
    char x1 : 1;
    char x2 : 1;
    char x3 : 1;
    char x4 : 1;
    char x5 : 1;
    char x6 : 1;
    char x7 : 1;
    char x8 : 1;
    unsigned int an_int;

} my_struct;

I want to modify the group made by the bits x3, x4, x5, x6 to value between 0 and 15, value read from stdin (and the rest of the values being 0).

How do I do that?

(for example, in int main() I have my_struct x_struct, and I want to modify x3, x4, x5, x6 of it). Any help?

Answer 1

#include <assert.h>
#include <stdlib.h>

typedef struct {
    char x1 : 1;
    char x2 : 1;
    char x3 : 1;
    char x4 : 1;
    char x5 : 1;
    char x6 : 1;
    char x7 : 1;
    char x8 : 1;
    unsigned int an_int;
} my_struct;


int main(int argc, const char* argv[])
{
    int input_value;
    my_struct x_struct;

    assert(argc == 2);
    input_value = strtol(argv[1], NULL, 10);
    assert(0 <= input_value && input_value < 16);

    x_struct.x3 = (input_value >> 0) & 0x01;
    x_struct.x4 = (input_value >> 1) & 0x01;
    x_struct.x5 = (input_value >> 2) & 0x01;
    x_struct.x6 = (input_value >> 3) & 0x01;

    return 0;
}