Printing 2d array initialized in a function but declared globally - c

Question

I am trying to print a 2d array that has been declared globally as a double pointer and initialized inside a function in main(), but I get a core dump error.
What am I doing wrong here?
The array stored in the file:
1 2
3 4
5 6
Code:
#include <stdio.h>
#include <stdlib.h>
int** matrix_A = 0;
void initArray ( int** matrixPtr, FILE* matrixFP, int row, int col );
int main ( int argc, char* argv[] )
{
FILE* matrixAfp = fopen ( argv[1], "r" );
int M = atoi ( argv[3] );
int N = atoi ( argv[4] );
initArray ( matrix_A, matrixAfp, 3, 2 );
for ( size_t m = 0; m < M; m++ )
{
for ( size_t n = 0; n < N; n++ )
{
printf ( "%d \n", matrix_A[m][n] );
}
}
return 0;
}
void initArray ( int** matrixPtr, FILE* matrixFP, int row, int col )
{
matrixPtr = ( int** ) malloc ( row * sizeof ( int* ) );
for ( size_t m = 0; m < row; m++ )
{
matrixPtr[m] = ( int* ) malloc ( col * sizeof ( int ) );
}
for ( size_t n = 0; n < row; n++ )
{
for ( size_t o = 0; o < col; o++ )
{
fscanf ( matrixFP, "%d", &matrixPtr[n][o] );
}
}
}

Answer 1

The problem is that since you're passing matrix_A to the function by-value, matrixPtr is actually a copy of the global matrix_A, which means all the changes inside the function are happening to matrixPtr and not to globally-defined matrix_A.
To solve this, you can instead pass it by-reference:
void initArray(int** &matrixPtr, FILE *matrixFP, int row, int col)
Apart from that, this:
int M = atoi(argv[3]);
int N = atoi(argv[4]);
should be:
int M = atoi(argv[2]);
int N = atoi(argv[3]);

Answer 2

You pass the pointer by value, not by reference, so whatever you do with matrixPtr inside initArray will not make a difference outside the initArray-function. Try to modify the initArray(FILE *matrixFP, int row, int col) as followed,
int * initArray(FILE *matrixFP, int row, int col){
int m,n,o;
int **matrixPtr = (int **)malloc(row * sizeof(int *));
for (m = 0; m < row; m++) {
matrixPtr[m] = (int *)malloc(col * sizeof(int));
}
for (n = 0; n < row; n++) {
for (o = 0; o < col; o++) {
fscanf(matrixFP, "%d", &matrixPtr[n][o]);
}
}
return matrixPtr;
}
And using matrix_A=initArray(matrixAfp, 3, 2); in the main() to do the function call should work.