multidimensional arrays in C (xcode 3.2.3)

Discussion in 'Mac Programming' started by bacteriatype4, Jun 6, 2011.

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  1. bacteriatype4, Jun 6, 2011

    bacteriatype4 macrumors newbie

    Joined:
    Jun 6, 2011
    #1
    I've been working on a project using my, now, old PC using visual C++.
    everything works fine there.

    Now i'm attempting to run it on my new iMac. however an strange error occurs.

    after allocating a simple 2d array

    Code:
    a = (int**) malloc(sizeof(int)*10);
	for(i=0;i<10;i++){a[i] = (int*) malloc(sizeof(int)*10);}
    when the following loop is processed

    Code:
    for(i=0;i<10;i++){for(j=0;j<10;j++){a[i][j]=0;}}
    EXC_BAD_ACCESS occurs. I made some research and i found something like there are holes in the memory or i should use a convention to a 1-dimensional array to deal with it. Another suggestions were around C++ object programing.

    it should work on simple C, but i don't know what is happening and i have plans to stay with macos =]
     
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  2. jiminaus, Jun 6, 2011

    jiminaus macrumors 65816

    jiminaus

    Joined:
    Dec 16, 2010
    Location:
    Sydney
    #2
    Your code is not 64-bit clean because of a coding error. It worked on 32-bit Window because a pointer is the same size an integer under that system. It's not true under 64-bit Mac OS X.

    Your missing an asterisk, highlighted below in red.
    Code:
    a = (int**) malloc(sizeof(int[COLOR=RED]*[/COLOR])*10);
	for(i=0;i<10;i++){a[i] = (int*) malloc(sizeof(int)*10);}
     
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  3. bacteriatype4, Jun 6, 2011

    bacteriatype4 thread starter macrumors newbie

    Joined:
    Jun 6, 2011
    #3
    amazing!

    thank you very much!
     
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  4. gnasher729, Jun 7, 2011

    gnasher729 macrumors G5

    gnasher729

    Joined:
    Nov 25, 2005
    #4
    General observation: When you write code, and it crashes, your very first assumption should be that there is a bug in your code, and you should stay with this assumption until it is proven wrong - and believe me, that is very, very unlikely to happen. Obviously the code would have crashed on _any_ compiler with 32 bit int and 64 bit pointers.
     
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  5. lee1210, Jun 7, 2011

    lee1210 macrumors 68040

    lee1210

    Joined:
    Jan 10, 2005
    Location:
    Dallas, TX
    #5
    Just to be a dick, anywhere the sizeof(void *) > sizeof(int).

    -Lee
     
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