Converting floating point to binary - c

Question

#include <stdio.h>
void printBinary(int n, int i) {
int k;
for(k = i-1;k>=0;k--){
if((n>>k)&1)
printf("1");
else
printf("0");
}
}
typedef union {
float f;
struct {
unsigned int mantissa : 23; //4
unsigned int exponent : 8; //3
unsigned int sign : 1;
}raw;
}myfloat;
void printIEEE(myfloat var){
printf("%d | ", var.raw.sign);
printBinary(var.raw.exponent,8); //3
printf(" | ");
printBinary(var.raw.mantissa, 23); //4
printf("\n");
}
int main(){
myfloat var;
var.f = -4.25;
printf("IEEE 754 represantation of %f is : \n",var.f);
printIEEE(var);
return 0;
}
I found this code from Internet. I get an error when I make some changes on it. For example, i want to change the number. I want to make 3 exponent and 4 mantissa when i change the number output is happening 0 000 0000.

Answer 1

Would you please try a cheat solution which share the bit pattern in the union:
#include <stdio.h>
#include <stdint.h>
union ieee754 {
uint32_t i;
float f;
};
void printBinary(uint32_t n, int i) {
uint32_t mask = 1 << (i - 1);
do putchar(n & mask ? '1' : '0');
while (mask >>= 1);
}
int main()
{
union ieee754 var;
var.f = -4.25;
printf("IEEE 754 represantation of %f is:\n", var.f);
printBinary(var.i, 32);
printf("\n");
return 0;
}
Output:
IEEE 754 represantation of -4.250000 is:
11000000100010000000000000000000
Interpretation (or verification) of the bit pattern:
11000000100010000000000000000000
sign bit ... 1
exponent ... 10000001 (= 129)
fraction ... 00010000000000000000000 (= 1/16)
decimal value = (-1)^1 * (1 + 1/16) * 2^(129 - 127))
= -4.250000