access violation (segmentation fault)

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  1. #1
    Village id10t
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    access violation (segmentation fault)

    Why does this code cause my program to crash with the error "access violation (segmentation fault)"? and what is it?
    Code:
    for (counter=0;counter<UsedSpace;counter++)
    {
       if (Numbers1[counter]<Numbers2[counter])
         {
         sort[counter]=Numbers1[counter];
         }
         else sort[counter]=Numbers2[counter];
    }
    thanks in advance

  2. #2
    C++ Witch laserlight's Avatar
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    Perhaps you are accessing an array out of bounds.
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  3. #3
    The larch
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    You are providing a bit too little info to answer that.
    Most probably you have out-of-bounds accesses. For example, is sort resized to UsedSpace.

    Anyway, if this is meant for merging two vectors, you'll need to figure out the algorithm first (for example, on paper).

    Something like this (X marks past end of array, if any of the pointers reaches that, you'll need to figure out something in addition):
    Code:
    1 2 5 X
    ^
    a
    
    3 4 7 X
    ^
    b
    
    
    
    a points to smaller. Pick *a and advance a.
    
    1 2 5 X
      ^
      a
    
    3 4 7 X
    ^
    b
    
    1
    
    a still points to smaller. Pick *a and advance it again.
    
    1 2 5 X
        ^
        a
    
    3 4 7 X
    ^
    b
    
    1 2
    
    Now b points to a smaller value. Pick *b and advance it.
    
    1 2 5 X
        ^
        a
    
    3 4 7 X
      ^
      b
    
    1 2 3
    
    etc.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  4. #4
    Village id10t
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    Ok thanks guys, guess its back to the drawing board. Again thank you

  5. #5
    C++まいる!Cをこわせ!
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    Here's another tip for you:
    Use std::vector if you aren't, then use the .at member function.
    If you try to access out-of-bounds, it will throw an exception.
    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.

  6. #6
    The larch
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    You are also probably better off adding items to Sort (which is initially empty) using push_back(), rather than indices.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  7. #7
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    But then you might want to precede the 'push_back' by a 'reserve' for efficiency...

  8. #8
    C++ Witch laserlight's Avatar
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    But then you might want to precede the 'push_back' by a 'reserve' for efficiency...
    Take a look at the last paragraph of Stroustrup's answer to the FAQ: Why are the standard containers so slow?
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