Thread: 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;
}

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

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.

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