Passing a 2d dynamic array of strings by reference in C++ - c++

Question

I have to use a dynamic array for this project but I can't pass it by reference, I am not sure what to do, I initialized the 2d dynamic array, but not sure how to pass it by reference.
#include <iostream>
#include <vector>
#include <string>
#include <iomanip>
using namespace std;
#define row 5
#define col 14
typedef string* StrArrPtr;
void set_up_array(string (&&layout_array)[row][col]);
int main()
{
StrArrPtr *layout_array = new StrArrPtr[col];
for(int i = 0; i < row; i++)
{
layout_array[i] = new string[col];
}
//string layout_array[row][col];
set_up_array(layout_array);
for(int i = 0; i < row; i++)
{
for(int j = 0; j < col; j++)
{
if(j == 1 && i > 0)
{
cout << right << setw(11);
}
cout << "| " << layout_array[i][j] << " ";
}
cout << "|" << endl;
}
return 0;
}
void set_up_array(string (&&layout_array)[row][col])
{
layout_array[0][0] = "Lab Number"; //First Column / first row
layout_array[1][0] = "1"; // second row
layout_array[2][0] = "2"; // third row
layout_array[3][0] = "3"; // fourth row
layout_array[4][0] = "4"; // fifth row
}
I am new to c++ so the solution might be very obvious but I just can't see it. Any help would be appreciated.

Answer 1

Given what you are doing with the array in set_up_array, you don't need to pass the actual string* by reference, because you're simply dereferencing it (telling your computer where to look for a string) and altering the value of string located at that index. When you pass an array in C/C++, you're just passing in an int, so don't worry about references unless you're modifying what the pointer is pointing to.
(It would be like string * &ref)

Answer 2

To pass a 2D array by reference, use:
void set_up_array(string (&layout_array)[row][col]);
In order to be able call that function, the variable needs to be of type string [row][col].
Change main to:
int main()
{
std::string layout_array[row][col];
set_up_array(layout_array);
...
}
Since you know the sizes of the arrays at compile time, it will be better to use std::array.
#include <iostream>
#include <vector>
#include <array>
#include <string>
#include <iomanip>
using namespace std;
const int row = 5;
const int col = 14;
void set_up_array(std::array<std::array<std::string, col>, row>& layout_array);
int main()
{
std::array<std::array<std::string, col>, row> layout_array;
set_up_array(layout_array);
for(int i = 0; i < row; i++)
{
for(int j = 0; j < col; j++)
{
if(j == 1 && i > 0)
{
cout << right << setw(11);
}
cout << "| " << layout_array[i][j] << " ";
}
cout << "|" << endl;
}
return 0;
}
void set_up_array(std::array<std::array<std::string, col>, row>& layout_array)
{
layout_array[0][0] = "Lab Number"; //First Column / first row
layout_array[1][0] = "1"; // second row
layout_array[2][0] = "2"; // third row
layout_array[3][0] = "3"; // fourth row
layout_array[4][0] = "4"; // fifth row
}

Answer 3

Arrays are always pass by reference.. your problem is how to pass a 2d array of string...
analyze how i did it:
#include <iostream>
#include <vector>
#include <string>
#include <iomanip>
using namespace std;
#define row 5
#define col 14
typedef string* StrArrPtr;
void set_up_array(string* layout_array[]);
int main()
{
StrArrPtr *layout_array = new StrArrPtr[row];
for(int i = 0; i < row; i++)
{
layout_array[i] = new string[col];
}
//string layout_array[row][col];
set_up_array(layout_array);
for(int i = 0; i < row; i++)
{
for(int j = 0; j < col; j++)
{
if(j == 1 && i > 0)
{
cout << right << setw(11);
}
cout << "| " << layout_array[i][j] << " ";
}
cout << "|" << endl;
}
return 0;
}
void set_up_array(string* layout_array[])
{
layout_array[0][0] = "Lab Number"; //First Column / first row
layout_array[1][0] = "1"; // second row
layout_array[2][0] = "2"; // third row
layout_array[3][0] = "3"; // fourth row
layout_array[4][0] = "4"; // fifth row
}