在C ++中通过引用传递2D动态字符串数组

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


}