Pass two dimensional array in function [duplicate] - c++

Question

This question already has answers here:
How to pass a 2D array by pointer in C?
(5 answers)
Closed 2 years ago.
I am trying to pass two dimensional array in function, but is has two errors which I don't know why. I have some articles about passing two dimensional array in function but also can't understand why I fail.
#include <iostream>
using namespace std;
// prototypes
void matrixSwap(double** matrix, int rows, int columns);
int main()
{
const int ROWS = 5;
const int COLUMNS = 5;
double matrix[ROWS][COLUMNS] =
{
{ 1, 2, 3, 4, 5},
{ 6, 7, 8, 9, 0},
{11, 12, 13, 14, 15},
{16, 17, 18, 19, 20},
{21, 22, 23, 24, 25}
};
matrixSwap(matrix, ROWS, COLUMNS);
/* it says
1) argument of type "double (*)[5U]" is incompatible with parameter of type "double **"
2) 'void matrixSwap(double *[],int,int)': cannot convert argument 1 from 'double [5][5]' to 'double *[]'
*/
}
void matrixSwap(double** matrix, int rows, int columns) {}

Answer 1

The multidimensional double array matrix you're trying to pass in the function matrixSwap() to the argument double**, actually doesn't represents a multidimensional array.
Use arrays correctly as shown:
#include <iostream>
using namespace std;
const unsigned short MAXROWS = 5;
// prototypes
void matrixSwap(double matrix[][MAXROWS], int rows, int columns);
int main()
{
const int ROWS = 5;
const int COLUMNS = 5;
double matrix[ROWS][COLUMNS] =
{
{ 1, 2, 3, 4, 5},
{ 6, 7, 8, 9, 0},
{11, 12, 13, 14, 15},
{16, 17, 18, 19, 20},
{21, 22, 23, 24, 25}
};
matrixSwap(matrix, ROWS, COLUMNS);
}
void matrixSwap(double matrix[][MAXROWS], int rows, int columns) {}
Just changed into [][MAXROWS] where MAXROWS contains an unsigned integer of value 5.
The declaration:
void matrixSwap(double matrix[][MAXROWS], int rows, int columns)
is equivalent to:
void matrixSwap(double (*matrix)[MAXROWS], int rows, int columns)
Notice that here I've used *matrix and then appended [MAXROWS] which does the same job as matrix[][MAXROWS].
So you may do the same thing in another way as follows:
void matrixSwap(double (*matrix)[MAXROWS], int rows, int columns) {
for (int i = 0; i < columns; i++) {
for (int j = 0; j < rows; j++) {
std::cout << matrix[i][j] << ' ';
}
std::cout << std::endl;
}
}
This will give you the output:
1 2 3 4 5
6 7 8 9 0
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
To see if the matrix is successfully passed into the function by the new argument.