在C中将整数转换为二进制字符串

Question

This is what I've tried, my logic is that my tmp shifting left 31 times will get compared to the user input integer I and a value of 1 or 0 will be inserted to index str[0] -> str[31] and the I null terminate str[32] with the \\0 .

However, I'm getting a segmentation fault.

PS I'm not allowed to change the parameters of this function and my professor set the size of str to be 33 in the main, which, I'm not allow to change either.

void int2bitstr(int I, char *str) {
        int tmp = 1 << 31;
        do{
                *str++ = !!(tmp & I) + '0';
        } while(tmp >>= 1);
        *str = '\0';
}

Answer 1

Try making tmp an unsigned int . The behaviour of right-shifting a negative (signed) integer is implementation-defined, and in your case is likely shifting in 1s (the original MSB) thus causing the loop to exceed the length of str .