Question

this program is written in C

it supposed to get a two D array( matrixAdd) and scan it with scanMtx (the scanning function isn’t here becuase the code isn’t relevant)

the problem: the EDMtx function return the scanning matrix 1,1,1,,1,-8,1,,1,1,1
when it return back to main it is : 0,0,0,0,0,0,junk,junk,junk

it seems that there is a address error

what did i do wrong?

#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>

struct matrix
{
    int* ptr;
    int row;
    int column;
};

matrix EDMtx();

void main( int argc, char* argv[])
{
    int matrixAdd[5][5]={{1,1,1,3,4},{1,1,1,3,4},{1,1,1,3,4},{1,1,1,3,4},{1,1,1,3,4}};
    matrix mtx;
    matrix scanMtx;

    mtx.ptr=&matrixAdd[0][0];
    mtx.row=5;
    mtx.column=5;

    scanMtx= EDMtx();

//  mtx= ScanM(mtx,1,1,scanMtx);- doesn't important to you.

    getchar();
}
matrix EDMtx()

{

    int matrx[3][3]={{1,1,1},{1,-8,1},{1,1,1}};
    matrix Mtx;

    Mtx.ptr=&matrx[0][0];
    Mtx.row=3;
    Mtx.column=3;

    return Mtx;
}

Answer 1

The variables matrixAdd and matrx, and the memory they point to, have local scope only. If you want them to persist after returning from a function, either declare them static, or redesign your code logic. (e.g. by using malloc to allocate memory explicitly)