can someone tell me why this creates a segmentation fault?

This is a discussion on can someone tell me why this creates a segmentation fault? within the C Programming forums, part of the General Programming Boards category; Code: include <stdio.h> void getSignMantissaExponent(float number, int* sign, unsigned int* mantissa, int* exponent){ int* second = (int *) &number; *sign ...

  1. #1
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    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;
    }

  2. #2
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    sign, mantissa and exponent aren't initialized

    Code:
    int* sign;
      int* exponent;
      unsigned int* mantissa;
    
      getSignMantissaExponent(first, sign, mantissa, exponent);

  3. #3
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    I want them to be initialized after the getSignMantissaExponent runs

  4. #4
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    so how would I do this?

  5. #5
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by -EquinoX- View Post
    so how would I do this?
    Don't declare them as pointers. Pass their addresses.

  6. #6
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    well this is a requirement in my assignment that I have to pass it in a pointers

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by -EquinoX- View Post
    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.

  8. #8
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    yeah that makes more sense.. thank you!

  9. #9
    Fountain of knowledge.
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    When do you make second a pointer to an int when it is given the addess of a float?

  10. #10
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    oh never mind I fixed it
    Last edited by -EquinoX-; 03-04-2008 at 07:15 PM.

  11. #11
    C++まいる!Cをこわせ!
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    So what are you trying to do? Your code does not find the correct exponent or mantissa.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  12. #12
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    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

  13. #13
    C++まいる!Cをこわせ!
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    Hmm. Yes, if you don't manipulate the mantissa & exponent, it's right.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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