对二维数组使用 scanf 时出现 C 分段错误

Question

As suggested by a book of "Gottfried", I tried to input an array and display the contents of array in matrix form :

#include<stdio.h>

#define row 2
#define col 3

int main(){
    int (*a)[col];
    int i,j;

    for(i=0;i<row;i++){
        for(j=0;i<col;j++){
            printf("Enter a(%d,%d)",i,j);
            scanf("%d",(*(a+i)+j));
        }
    }

    return 0;
}

I get the following output after inputting an element :

Segmentation fault (core dumped)

What is the problem in the code? Was it working in previous version of GCC so the writer wrote it down? What is the correct way to solve the problem with the same level of simplicity?

Answer 1

As it was pointed out in the comments it is not a 2D array, but a 1D array of pointers. Also in the second for loop you accidently use i<col instead of j<col . This will work

#include<stdio.h>

#define ROW 2
#define COL 3

int main(){
    int a[ROW][COL];
    int i, j;

    for(i = 0; i < ROW; i++){
        for(j = 0;j < COL; j++){
            printf("Enter a(%d,%d)", i, j);
            scanf("%d", (*(a + i ) + j));
        }
    }
    return 0;
}

Answer 2

If you want to declare a as a pointer to an array of col int s, as it's done in this line

int (*a)[col];

Then you should also allocate (and ultimately free) the memory needed, before trying to use it.

a = malloc(sizeof(*a) * row);
if (!a)
    exit(1);
// ...
free(a);

The posted code also have another issue in the nested loops

for (i = 0; i < row; i++) {
    for (j = 0; i < col; j++) {
//              ^^^^^^^           It should be 'j < col'