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MSVS has triggered a breakpoint

This is a discussion on MSVS has triggered a breakpoint within the C Programming forums, part of the General Programming Boards category; Hi guys, We are just learning how to implement calloc, malloc and free. At the end of my program, I ...

  1. #1
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    MSVS has triggered a breakpoint

    Hi guys,

    We are just learning how to implement calloc, malloc and free. At the end of my program, I keep getting a "windows has triggered a break point" error. Im pretty sure that this error is happening because of the way I am implementing free because this is the error I am getting in free.c - " retval = HeapFree(_crtheap, 0, pBlock);"

    here is the code which I allocate and free memory:

    Code:
    int main (){
         
        WORDS userWords[16];
        char **board;
        int i=0, n=0, numWords=0;
        srand(time(NULL));
          numWords = enterWords(userWords);
    
    
        board = (char **) calloc(20, sizeof(char));
        for (i=0; i<20; i++){
            board[i] = (char *) calloc(40, sizeof(char));
        }
        for(i=0; i<20; i++)
        {
            if(i != 0)
                printf("\n");
            for(n=0; n<40; n++){
                board[i][n] = '0';
                printf("%c", board[i][n]);
            }
        }
        
        inputWords(userWords, board, numWords);
        cls;
        for(i=0; i<20; i++)
        {
            if(i != 0)
                printf("\n");
            for(n=0; n<40; n++){
                printf("%c", board[i][n]);
            }
        }
        pause;
        populateGameBoard(userWords, board);
        displayGameBoard(userWords, board, numWords);
        pause;
        free(board);
        return 0;
    }

  2. #2
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    We are just learning how to implement calloc, malloc and free. At the end of my program, I keep getting a "windows has triggered a break point" error. Im pretty sure that this error is happening because of the way I am implementing free because this is the error I am getting in free.c - " retval = HeapFree(_crtheap, 0, pBlock);"
    When people say they are implementing a function, they usually mean that they are writing that function. It doesn't look like you are creating your own custom malloc, calloc, and free functions. I am assuming you meant that you are learning to use these functions rather than implementing custom versions of them.

    Code:
        board = (char **) calloc(20, sizeof(char));     
        for (i=0; i<20; i++){         
            board[i] = (char *) calloc(40, sizeof(char));     
        }
    You're not allocating enough space for board. board is a pointer to a char pointer. sizeof (char) = 1. Unless you're on some obscure system, sizeof (char *) will most likely be larger than that on your system.

    Try this:
    Code:
        board = calloc (20, sizeof (char *)) ;
        for (i=0; i<20; i++) {         
            board [i] = calloc (40, sizeof (char)) ;
        }
    I didn't look at the rest of your code.
    Last edited by failure67; 04-06-2013 at 07:54 PM.
    Salem likes this.

  3. #3
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    I am getting "a value of type void* cannot be assigned to entity of type char**" with that calloc declaration. Is that because I declared char **board?

    Thanks

  4. #4
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    Thanks Failure67,

    I got it to work with this:
    Code:
    board = (char **)calloc (20, sizeof (char* )) ;
    for (i=0; i<20; i++) {         
         board [i] = (char *)calloc (40, sizeof (char)) ;
    }
    I still don't quite understand why. It looks like I am allocating 40 bytes to every value of i. Its not giving me the break error anymore though.

  5. #5
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    I am getting "a value of type void* cannot be assigned to entity of type char**" with that calloc declaration. Is that because I declared char **board?
    My bad, I skipped the fact you're using MSVS. MSVS is a c++ compiler, and the c++ language requires the casts that you added to your code. Pure C does not require (or recommend) those casts.

    I still don't quite understand why. It looks like I am allocating 40 bytes to every value of i. Its not giving me the break error anymore though.
    The problem was specifically with this part:

    Code:
    board = (char **) calloc(20, sizeof(char));
    Because sizeof (char) < sizeof (char *), you have not allocated enough memory for 20 pointers. That's why you had to change it to this:

    Code:
    board = (char **)calloc (20, sizeof (char* )) ;
    You also have a memory leak in your code. You have to free the 40 byte buffers that each of these 20 pointers pointed to.

    So you need to add something like this to the end of your code:

    Code:
    for (i = 0; i < 20; ++i) {
        free (board [i]) ; // Free the 40 byte buffers of each pointer
    }
    
    free (board) ; // Free the array of pointers

  6. #6
    and the hat of wrongness Salem's Avatar
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    Then you should name your source files to be prog.c, not prog.cpp.
    This should give the compiler driver the clue to use the C rather than C++ compiler.

    Or use this flag to force language choice.
    /Tc, /Tp, /TC, /TP (Specify Source File Type) (C++)
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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