Thread: can someone tell me why this creates a segmentation fault?

Code:

include <stdio.h>

void getSignMantissaExponent(float number, int* sign, unsigned int* mantissa, int* exponent){
  int* second = (int *) &number;
  *sign = (*second) & 0x80000000; /* note one ampersand for bitwise-and */
  *sign = *sign >> 31;

  if (*sign == 0)
    *sign = 1;
  else
    *sign = -1;

  *exponent = (*second) & 0x7F800000;
  *exponent = *exponent >> 23;
  *exponent = *exponent - 127;

  *mantissa = (*second) & 0x7FFFFF;
  *mantissa = *mantissa | 0x800000;

  printf("Sign bit is %d\n", *sign);
  printf("Exponent is %d\n", *exponent);
  printf("Mantissa is %x\n", *mantissa);
}


int main()
{
  float first = -10;
  int* sign;
  int* exponent;
  unsigned int* mantissa;

  getSignMantissaExponent(first, sign, mantissa, exponent);

  return 0;
}

sign, mantissa and exponent aren't initialized

Code:

int* sign;
  int* exponent;
  unsigned int* mantissa;

  getSignMantissaExponent(first, sign, mantissa, exponent);

I want them to be initialized after the getSignMantissaExponent runs

so how would I do this?

Originally Posted by -EquinoX-

so how would I do this?

Don't declare them as pointers. Pass their addresses.

well this is a requirement in my assignment that I have to pass it in a pointers

Originally Posted by -EquinoX-

well this is a requirement in my assignment that I have to pass it in a pointers

What we mean is that you don't actually have any space to put the mantissa once you compute it. You have a pointer, but you don't own the memory address it points to. So declare variables sign, exponent, and mantissa, and pass &sign, &exponent, and &mantissa to your function.

yeah that makes more sense.. thank you!

When do you make second a pointer to an int when it is given the addess of a float?

do you mean it does not because I substract it with 127 on the exponent and on the mantissa I added the hidden bit 1 by using the or?? because that's what I want to do