problem using pointer

This is a discussion on problem using pointer within the C Programming forums, part of the General Programming Boards category; what would cause the address saved in a pointer been changed when I am not doing any operation on that ...

  1. #1
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    problem using pointer

    what would cause the address saved in a pointer been changed when I am not doing any operation on that pointer?

    consider the following situation:

    I have 2 pointers, let's say a and b.
    a points to a address which is acquired by malloc, let's say 0x100ef
    and now, when I am doing some operation on pointer b, the address that is pointed
    by a is suddenly changed, let's say a is pointing to 0x0033 now.

    Is there any special details that I should take care when using pointer which I missed?

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    I could think of a few things I suppose (scope issues, fiddling with b when b points to a), but it would be easier to tell if you could cough up some details, ideally the actual code.

  3. #3
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    Quote Originally Posted by ptmstart View Post
    what would cause the address saved in a pointer been changed when I am not doing any operation on that pointer?
    Assuming there isn't a compiler bug involved (compiler bugs happen in approximately 1 in a million of these cases), the reason that a pointer is modified when another pointer is changed is because the second pointer holds the address of the first pointer - either on purpose or by accident.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Buffer overruns are a good example: http://cpwiki.sf.net/Buffer_overrun
    It you want to get to the bottom of it, it can take some good debugging. Fortunately, Visual Studio can help you catch these bugs very, very easily.
    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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