Printing matrix from an txt file in C - c

Question

I have to read the number of rows and columns of a matrix from a txt file also its elements. the first row is the number of rows and columns followed by its numbers. For example this is a matrix with 2 rows and 3 columns containing 123 456 and a matrix with 3 rows and 2 columns.
2 3
1 2 3
4 5 6.
3 2
1 2
3 4
5 6
What I have to do is to read two matrix from the same text file and multiply them. I'm encountering some unknown problem.
When I write my code to test whether the matrix is populated correctly. I only get the first matrix printed and then the program stopped. Output: 1 2 3
4 5 6
Here's the part of the code. Thanks in advance.
int main(){
int **mat1,**mat2,**result;
int row1,col1,row2,col2;
int i,j,k;
FILE *file;
char fname[100];
printf("enter file name\n");
scanf("%s", &fname);
file=fopen(fname, "r");
fscanf(file, "%d %d", &row1,&col1);//row of first matrix
mat1=malloc(row1 * col1 * sizeof(int*));//create memory for first matrix
//reading data for first matrix
for(i=0; i<row1; i++)
{
for(j=0; j<col1; j++)
{
fscanf(file, "%d", &mat1[i][j]);
}
}
for(i=0; i<row1; i++)
{
for(j=0; j<col1; j++)
{
printf("%d\t",mat1[i][j]);
}
printf("\n");
}
fscanf(file,"%d %d", &row2, &col2);//row of second matrix
mat2=malloc(row2 * col2 * sizeof(int*));//create memory for second matrix
//reading data for second matrix
for(i=0; i<row2; i++)
{
for(j=0; j<col2; j++)
{
fscanf(file,"%d",&mat2[i][j]);
}
}
for(i=0; i<row2; i++) //check mat2
{
for(j=0; j<col2; j++)
{
printf("%d\t",mat2[i][j]);
}
printf("\n");
}

Answer 1

I think I fixed the problem, but I had to do quite a bit of debugging due to lots of segfaults, so I'll put the answer to the original question at the top and defer all the things I had to debug to the bottom.
fscanf(file, "%*[.]"); //this is to read the period in the file
fscanf(file,"%d %d", &row2, &col2);//row of second matrix
mat2=malloc(row2 * col2 * sizeof(int*));//create memory for second matrix
By adding that one line of code, it started working for me, but it only started working due to the debugging below.
Since the number of calls to malloc did not represent the number of nested ararys that were indexed, I had to change the declaration of the matrices, the way they were populated, and they way they are referenced.
int *mat1,*mat2;
This declaration is to make the next edits work.
//reading data for first matrix
for(i=0; i<row1; i++)
{
for(j=0; j<col1; j++)
{
fscanf(file, "%d", &(mat1[i*col1 + j]));
}
}
for(i=0; i<row1; i++)
{
for(j=0; j<col1; j++)
{
printf("%d\t",mat1[i*col1 + j]);
}
printf("\n");
}
And of course, for the second matrix;
//reading data for second matrix
for(i=0; i<row2; i++)
{
for(j=0; j<col2; j++)
{
fscanf(file,"%d",&(mat2[i*col2 + j]));
}
}
for(i=0; i<row2; i++) //check mat2
{
for(j=0; j<col2; j++)
{
printf("%d\t",(mat2[i*col2 + j]));
}
printf("\n");
}
Please keep in mind that if you are going to be referencing an array inside of an an array, then you need to malloc space for another array in each slot of the original array. I chose the unintuitive approach to matrix arithmetic, but the code can be augmented to easily allow for double array indexing to be used.

Answer 2

You have some problem with allocating a 2D arrays:
For example:
mat1=malloc(row1 * col1 * sizeof(int*));//create memory for first matrix
it should be
mat1=(int**)malloc(row1 * sizeof(int*));//create memory for first matrix
Then should allocate each row in mat1 in for loop with before scanf each cell in a matrix
for (i = 0; i < row1; i++)
{
mat1[i] = malloc(col1 * sizeof(int));
for (j = 0; j < col1; j++)
{
fscanf(file, "%d", &mat1[i][j]);
}
}
Then, do similar stuff for mat2
Here is my solution that based on original problem:
#include <stdio.h>
#include <stdlib.h>
int main() {
int **mat1, **mat2, **result;
int row1, col1, row2, col2;
int i, j, k;
FILE *file;
char fname[100];
printf("enter file name\n");
scanf("%s", &fname);
file = fopen(fname, "r");
fscanf(file, "%d %d", &row1, &col1);//row of first matrix
mat1 = (int **)malloc(row1 * sizeof(int*));//create memory for first matrix
//reading data for first matrix
for (i = 0; i < row1; i++)
{
mat1[i] = malloc(col1 * sizeof(int));
for (j = 0; j < col1; j++)
{
fscanf(file, "%d", &mat1[i][j]);
}
}
for (i = 0; i < row1; i++)
{
for (j = 0; j < col1; j++)
{
printf("%d\t", mat1[i][j]);
}
printf("\n");
}
fscanf(file, "%d %d", &row2, &col2);//row of second matrix
mat2 = (int **)malloc(row2 * sizeof(int*));//create memory for second matrix
//reading data for second matrix
for (i = 0; i < row2; i++)
{
mat2[i] = malloc(col2 * sizeof(int));
for (j = 0; j < col2; j++)
{
fscanf(file, "%d", &mat2[i][j]);
}
}
for (i = 0; i < row2; i++) //check mat2
{
for (j = 0; j < col2; j++)
{
printf("%d\t", mat2[i][j]);
}
printf("\n");
}
fclose(file);
return 0;
}