printf a int/float pointer

This is a discussion on printf a int/float pointer within the C Programming forums, part of the General Programming Boards category; Hi I have this function which returns a void pointer: Code: printf( "value is %d\n", (int*)getSomething(input) ) ; printf( "value ...

  1. #1
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    printf a int/float pointer

    Hi

    I have this function which returns a void pointer:

    Code:
    printf( "value is %d\n", (int*)getSomething(input) ) ;
    printf( "value is %f\n", (float*)getSomething(input1) ) ;
    This doesn't work because %d and %f do not expect a pointer. So I changed the code to

    Code:
    printf( "value is %d\n", *(int*)getSomething(input) ) ;
    printf( "value is %f\n", *(float*)getSomething(input1) ) ;
    When I execute the code I get an Bus Error. Why doesn't this work and what is the solution ?

    thnx a lot!
    Luca

  2. #2
    Registered User claudiu's Avatar
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    If you want to print the address of the void pointer just print the return value of the function and use %p for formatting.

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    I need the value

  4. #4
    Registered User claudiu's Avatar
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    Well, you cannot dereference a void*. What you can do is cast it to an int* for example (if you are trying to get the int value pointed at) and dereference that.

    Haven't tried this in a while so I don't remember if it works, but try it out.

    Code:
    printf("%d", (*(int*)(something(input))));

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    You can't dereference void pointers since they have no size. Change your function to return the type that you are actually returning.

  6. #6
    Registered User claudiu's Avatar
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    Just tried my code above and it works for me.

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    it works for me too

    But, can someone explain the differences between:

    Code:
    printf( "value is %d\n", *(int*)getSomething(input) ) ;
    ,
    Code:
    printf( "value is %d\n", *((int*)getSomething(input)) ) ;
    and
    Code:
    printf( "value is %d\n", (*(int*)getSomething(input)) ) ;
    To me, these 3 might all dereference the int value!

  8. #8
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    Quote Originally Posted by jeanluca View Post
    To me, these 3 might all dereference the int value!
    That's because the three are exactly the same....

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    Thats a good thing (I thought I had Bus errors with the other 2)

    thnx!!

  10. #10
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    Quote Originally Posted by jeanluca View Post
    Thats a good thing (I thought I had Bus errors with the other 2)

    thnx!!
    Actually, that might very well be a bad thing. Because it probably means you have another unfixed flaw in there now.

  11. #11
    Registered User claudiu's Avatar
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    EVOEx is correct. Perhaps your problem was in whatever you were doing in that function and not in printing its return value.

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    I see the 3 running perfectly right now, so the bus error was indeed something else at that time!

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