Reading a file to matrix in C

Question

I get

"Debug assertion failed"

error when I try to compile this code.

Can someone please explain what is wrong with it? I think I've done something wrong with fscanf function. Thank You.

#include<stdio.h>
#include<stdlib.h>
#include<malloc.h>
void input(FILE *fp, int **a,int m)
{
    int i,j;
    for(i=0;i<m;i++)
    {
        for(j=0;j<m;j++)
        {
            fscanf(fp, "%d\n", *(a+i)+j);
        }
    }
}

int main()
{
    FILE*fp;
    int m,n,**a,i,j;
    scanf("%d",&m);
    fp=fopen("abc.txt","r");
    a=(int**)malloc(m*sizeof(int*));
    for(i=0;i<m;i++)
        *(a+i)=(int*)malloc(m*sizeof(int));
    input(fp,a,m);
    for(i=0;i<m;i++)
    {
        for(j=0;j<m;j++)
        {
            printf("%d ",*((a+i)+j));
        }
        printf("\n");
    }
    free(a);
    return 0;
}

Answer 1

There are several issues here, but to directly answer your question, you are not providing an address to fscanf() where it will store the integer it finds.

Without knowing your intent, I'll give an example:

fscanf( fp, "%d\n", &(a[i]) );

That says the ith element of array a is the one to be (over)written. So if a[i] is an int pointer, you might pass &( (a[i])[j] ) in there.

Also, I think you meant to replace:

*(a+i)=(int*)malloc(m*sizeof(int));

with

a[i] = (int*) malloc(m*sizeof(int));

Answer 2

The other comments and answers already pointed out what is not ok. So I skip it (fscanf(...), free, etc.).

The corrected version.

#include<stdio.h>
#include<stdlib.h>
#include<malloc.h>

void input(FILE *fp, int **a, int m) {
    int i, j;
    for (i = 0; i < m; i++) {
        for (j = 0; j < m; j++) {
            fscanf(fp, "%d\n", &a[i][j]);
        }
    }
}

int main() {
    FILE *fp;
    int m, n, **a, i, j;
    scanf("%d", &m);
    fp = fopen("abc.txt", "r");
    a = (int**) malloc(m * sizeof (int*));
    for (i = 0; i < m; i++)
        a[i] = (int*) malloc(m * sizeof (int));
    input(fp, a, m);
    for (i = 0; i < m; i++) {
        for (j = 0; j < m; j++) {
            printf("%d ", a[i][j]);
        }
        printf("\n");
    }
    for (i = 0; i < m; i++)
        free(a[i]);
    free(a);
    return 0;
}