在C中动态分配2D数组

Question

I've been reading around and I've been applying what I've been reading to my code but I am not sure if I am missing something.. the 2d array is suppose to mirror sudoku. I know the problem area is in my arrayMake function. My professor recommended using a cast with the malloc call so: sudoku = (int**)malloc(sudokus*sizeof(int*)); but that did not work for me.

int main(){
    int sudokus;
    int** sudoku;
    sudokus = getUserInfo();
    sudoku = arrayMake(sudokus);
    /*for (int i = 0; i < (SIZE*sudokus), i++;){
        for (int j = 0; j < SIZE, j++;){
            printf("Numbers[%d][%d]:%d", i, j, sudoku[i][j]);
        }
    }*/
    system("pause");
    return 0;
}

int getUserInfo(){
    int sudokus;
    printf("How many Sudokus are you checking today?\n");
    scanf("%d{^\n]\n", &sudokus);

    return sudokus;
}

int** arrayMake(int sudokus){
    int **sudoku;
    int realsize;
    realsize = 9 * sudokus;

    sudoku = malloc(realsize*sizeof(int*));
    if (sudoku == NULL){
        printf("Memory allocation failed");
        return 0;
    }
    for (int i = 0; i < realsize, i++;){
        sudoku[i] = malloc(9 * sizeof(int));

        if (sudoku[i] == NULL){
            printf("Memory allocaiton failed");
            return 0;
                            }

    }

    return sudoku;
}

Answer 1

My professor recommended using a cast with the malloc call so: sudoku = (int**)malloc(sudokus * sizeof(int*)); but that did not work for me.

To dynamically allocate for 2D array, you usually need to do two steps. Your code is not clear as you include a realsize = 9 * sudokus which doesn't make sense. Anyway, for simplicity, lets assume your sudoku is a 3x3 matrix. You'll need to:

1. Allocate for the pointer to pointer to int:

    int **sudoku = malloc( 3 * sizeof( int * ) ); 

2. Allocate for each of the individual pointer to int:

    for( int i = 0; i < 3; i++ ) sudoku[i] = malloc( 3 * sizeof( int ) ); 

Answer 2

From what I see your problem exists in your for loops where you have:

for (i = 0;i < realsize , i++)

when you really meant:

for (i = 0;i < realsize ; i++) ^ Note the change of , to ;

Answer 3

scanf("%d{^\\n]\\n", &sudokus); is a mistake.

I guess you meant the { to actually be a [ but the format string is still wrong even after that change. I think you intended to consume the rest of the input, up to and including a newline character. However, your format string does not actually do that.

Scanf'ing for \\n actually means consume any amount of whitespace , so in fact this code (with the [ fix) would continue waiting for input until there was a newline, and also another non-whitespace character typed after the newline.

Better would be:

scanf("%d", &sudokus);
int ch;
while ( (ch = getchar()) != '\n' && ch != EOF ) { }

There are a few different ways to achieve the same goal. (Note that scanning for %d[^\\n]%c is not one of them; that string is also broken).

Also I would suggest a different variable name than sudokus . It's confusing having two similarly-named variables sudoku and sudokus . Name it something that reflects its meaning.

---

For allocating your array, it would be much simpler to take out the arrayMake function and write something like:

int sudoku[9][9];

(I couldn't figure out what sudokus was supposed to mean or what realsize was going to be, but you could put your intended dimension inside the square brackets there).