动态 memory 分配矩阵写为结构

Question

I need to allocate memory for a struct that contains a matrix:

typedef struct matrix{
int row;
int column;
int **data;
}MATRIX;

And i need to do all of it inside one separate function. I'm a bit confused because I'm not sure on how am I supposed to allocate memory for a matrix [row*column] that is inside of a struct that also contains numerical information about the row and column size. By my (obviously flawed) logic, that'd mean I'd need to allocate memory for the struct, input the info on row and column size, and then additionaly allocate memory for the matrix that's indside of a struct. I'm a bit confused by it, but this is what I've come up with so far:

int** alloc(MATRIX *array , int row , int column){

int i;

array->data = (int**)malloc(row * sizeof(int*));

for(i=0; i<br_red; i++){
    array->data[i] = (int*)malloc(column * sizeof(int));
}
return array->data;
}

And then inside of main() I do:

MATRIX *array = (MATRIX*)malloc(sizeof(MATRIX));
scanf("%d" , &array->row);
scanf("%d" , &array->column);
array->data = alloc(array , array->row , array->column);

And this code works properly, but my task is to completely allocate the memory for all data inside of one function of MATRIX* type (that returns fully allocated struct + matrix) without ever jumping back to main() to do the scanning.

Answer 1

You can change your alloc function to allocate a MATRIX internally and return it as the function result, like so:

MATRIX* alloc (int row , int column)
{
    MATRIX *array = (MATRIX *) malloc (sizeof (MATRIX));
    array->data = (int**)malloc(row * sizeof(int*));
    for (int i = 0; i < row; i++)
        array->data[i] = (int*)malloc(column * sizeof(int));
    return array;
}

Your main then becomes:

int row, column;
scanf("%d" , &row);
scanf("%d" , &column);
MATRIX *array = alloc (row, column);

The casts before malloc are not necessary (in C), but they are harmless.