C++ - Passing array from function to function

Question

So I have this code:

main.cpp

#include "matrix.h"

int main(int argc, char *argv[])
{


    matrix m;
    regularMatrix rMatrix;

    rMatrix.setDetails(3, "1 2 3 4 5 6 7 8 9");
    //rMatrix.displayMatrix();

    //int i, j, r = 0, c = 0, a;


    //cout << "Enter number of Rows and Columns: " << endl;

    //cin >> r ;












    system("PAUSE");
    return EXIT_SUCCESS;
}

matrix.cpp

#include "matrix.h"

int rows = 3, columns = 3;
int **a;




void matrix::displayMatrix(int **arr)
{

    cout  <<  "Values Of 2D Array [Matrix] Are : ";
    for  (int i  =  0;  i  <  rows;  i++  )
    {
         cout  <<  " \n ";
         for  (int j  =  0;  j  <  columns;  j++  )
         {
              cout <<  arr[i][j] << "    ";
         }
    }
}

void matrix::setDetails(int dimension, string y)
{
     int f = dimension;
     rows = dimension;
     columns = rows;
     string input = y;

     istringstream is(input);
     int n;

     a = new int *[rows];
     for(int i = 0; i <rows; i++)
     {
             a[i] = new int[columns];
     }   



     for  ( int i  =  0;  i  <  rows;  i++  )
     {
          for  ( int j  =  0;  j  <  columns;  j++  )
          {
               while ( is >> n)
               {
                     a[i][j] = n;
                     //cout << a[i][j] << endl;
               }
          }
     }



     matrix::displayMatrix(a);

     //cout << f << endl << g << endl;
}

matrix.h

#include <cstdlib>
#include <iostream>
#include <string>
#include <sstream>

using namespace std;

class matrix
{
      public:
             virtual void displayMatrix(int** arr);
             virtual void setDetails(int dimension, string y);
             //virtual void setMatrix(int m[]);
             //virtual void printArray(int** i);


};

class regularMatrix : public virtual matrix
{
      public:


};

It runs without error but the problem is, I'm getting different value when I'm displaying the matrix? I think I'm getting the address of the array.How will I get the value out of it? I think I'm right about passing my array.

Consider using debugger tool with watches window open and go through the code step by step. It's really good in dealing with this sort of problems — alexeykuzmin0
– alexeykuzmin0, Commented Aug 31, 2016 at 11:19
Consider also using std::vector instead of arrays. All these woes (including the memory leak you're not seeing there) will go away :). — The Marlboro Man
– The Marlboro Man, Commented Aug 31, 2016 at 11:20
Can you provide a minimal reproducible example that reproduces you problem please. Also add information about what you observed during debugging your code. It's likely that you output uninitialzezed values from arr[i][j] rather then addresses. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Aug 31, 2016 at 11:21
you can always get a c-style array from a vector when needed, thus even if you have to pass arrays, I would always use a vector in my code (or std::array when appropriate) — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Aug 31, 2016 at 11:22

MindRoller · Accepted Answer · 2016-08-31 11:32:30Z

1

 for  (  i  =  0;  i  <  rows;  i++  )
 {
      for  (  j  =  0;  j  <  columns;  j++  )
      {
           while ( is >> n)
           {
                 a[i][j] = n;
                 //cout << a[i][j] << endl;
           }
      }
 }

This is actually pretty wrong. Look what you're doing here. At beggining, you have i = 0 and j = 0

Then you got into the while loop.

And here until you input ints from stringstream you assign a[0][0] to new value. See it? You never go to a[0][1] etc. Only first element will be valid and the rest will stay uninitialized, because after first execution of your while loop there is no characters left in the istringstream object.

So to correct it:

for  (  i  =  0;  i  <  rows;  i++  )
     {
          for  (  j  =  0;  j  <  columns;  j++  )
          {
              if ( is >> n )
              a[i][j] = n;
          }
     }

edited Aug 31, 2016 at 11:32

answered Aug 31, 2016 at 11:29

MindRoller

2414 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

MindRoller Over a year ago

No problem, I added a code that should be helpful if you encountered some problems, however I am pretty sure that you already solved it yourself.

Zelgh Over a year ago

Thanks for the correction, I didn't think about that!

Collectives™ on Stack Overflow

C++ - Passing array from function to function

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related