Bit setter

bi.c

#include <stdio.h>
#include <stdlib.h>

void setbit(int* data, char from, char len, int val)
{
    unsigned int b = ~0;
    b >>= sizeof(int)*8 - len;
    *data &= ~(b << from-len);
    *data |=  (val << from-len);
}

void print_bits(int data)
{
    int a = sizeof(int)*8;
    unsigned int mask = ~0;
    mask <<= sizeof(int)*8 - 1;
    while(a) {
        printf("%d", (data & mask) ? 1 : 0);
        data <<= 1;
        --a;
    }
}

int main(int argc, char* argv[])
{
    int value = atoi(argv[1]);
    printf("val: %5d, 0x%04x, 0b", value, value);
    print_bits(value);
    puts("");
    if (argc == 5) {
        int vls[3] = { atoi(argv[2]), atoi(argv[3]), atoi(argv[4]) };
        setbit(&value, vls[0], vls[1], vls[2]);
        printf("val: %5d, 0x%04x, 0b", value, value);
        print_bits(value);
        puts("");
    }

    return 0;
}