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I have a matrix saved in a .txt file, it has values, I created a function that takes row and number as parameters, then it returns the value obtained from the matrix.txt file.
I have a 2D array containing pairs of rows/columns, they are not ordered also they are random pairs, How could I iterate overe this 2D array and pass each pair to the function getList(rw,cl) to obtain such a file as result.

row,column,its value
row,columm,its value

Thanks for any help, notice please I am still beginner, so no advances tips

What I have tried:


using namespace std;

const int col_nbr = 7;
const int row_nbr = 3;

int static getValueOf[col_nbr][row_nbr];      
void loadMatrix(){

int x, y;

ifstream in("/storage/emulated/0/matrix.txt");

//This my matrix .txt file saved in pc    
11 12 13 14 15 16 17
21 22 23 24 25 26 27
31 32 33 34 35 36 37

if (!in){
    cout << "Cannot open file.\n";

  for (x = 0; x < row_nbr; x++){       
     for (y = 0; y < col_nbr; y++){
       in >> getValueOf[x][y];


int getList(int rw,int cl){

return getValueOf[rw-1][cl-1];

int main(){


//I would take each pair row/columm from this 2D array coords, then I pass the row and the columm to the function getList(rw,cl) to get a list of the coorespondent values from the matrix.txt

int coords [4][2] = {{3,0},{2,1},{6,2},{1,1}};
//int coords has 4 rows and 2 columms

    cout<<getList(1,1)<<endl;  //11
    cout<<getList(3,7)<<endl;  //37

return 0;
Updated 3-Jul-18 22:48pm
Mohibur Rashid 3-Jul-18 20:54pm    
I am kinda skeptical right now. You can create a nested loop for reading from file but cannot create a single loop?
Patrice T 3-Jul-18 22:03pm    
not clear!
give details of problem.
khaledce 4-Jul-18 6:47am    
@ppoymorphe, ok, then let's forget everything above for a moment and say, we have a function getList(row,columm), it returns a singe int value; and a 2D array in the .cpp file, it has 4 couples of pair row/column.
How to iterate getList(row,column) via two nested for-loops over the 2D array, in order to get the correspondent values for these couples, to be stored in a new 1D array or in external file, doesn't matter

1 solution

What about abandoning global variables and using modern C++ features and library?
(pass your data file as stdin, using input redirection).
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <array>
using namespace std;

using Matrix = vector < vector <int > >;

int main()
  Matrix m;
  string line;
  while ( getline( cin, line) )
    vector <int> row;
    istringstream iss(line);
    while ( iss )
      int i;
      iss >> i;
    m.push_back( row );

  array< array <int, 2>, 4> arr{{{3,0},{2,1},{6,2},{1,1}}};

  for ( const auto & a : arr)
    int r = a[1]; // it looks there is some confusion on 'rows' and 'columns' interpretation...
    int c = a[0];
    cout << "M[" << r << "," << c << "]= " << m[r][c] << "\n";
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