How to send a 2D array to a function?

Question

I'm trying to pass a 2D matrix with dimensions entered by the user to a function, for example arrayTest[r][c]. I've done my research and cannot find an answer that works. I'm using codeblocks on windows if that matters.

My Code:

#include <iostream>

using namespace std;
int r, c;

template <size_t r, size_t c>
void printMatrix(double (&matrix)[r][c])
{
    for(int i=0;i<r;i++)
    {
        for(int j=0;j<c;j++)
        {
             cout<<matrix[i][j]<<" ";
        }
        cout<<endl;
    }
}

int main()
{
    r = 1;
    c = 1;
    double matrix[r][c] = { { } };
    printMatrix(matrix);
    return 0;
}

I currently get the error: no matching function for call printMatrix.

`std::array` is a far better option than a C-style array (or `std::vector` if you need dynamic resizing). — Jesper Juhl, Jul 20 '17 at 18:36
You're better off with an std::vector and calculating the offset by hand. Otherwise you can get a ragged array, plus the overheads are greater. — Malcolm McLean, Jul 22 '17 at 16:15

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

with dimensions entered by the user
double matrix[r][c]

The size of an array variable must be known at compile time, and therefore can not be entered by the user.

However, you can allocate the array dynamically. Dynamic memory management is quite tricky to get right, and it is best to abstract it away in a container object.

There already exists an implementation of dynamic array container in the standard library: std::vector. The type of the elements of the vector is a template argument, so you can use a vector of vectors to represent an array of arrays i.e. a 2D array.

score 0 · Answer 2 · edited Sep 25 '17 at 04:13

0

In C++, you should be using std::vector instead of C-style arrays. By the way for your current problem, you can visit here passing 2-d array to a function. Hope it helps. Also you need to input the values of variables r and c before passing (&matrix)[r][c] to the function printMatrix().

edited Sep 25 '17 at 04:13

Jonathan Leffler

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answered Jul 20 '17 at 17:30

SSM

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Sam · Answer 3 · 2017-07-22T15:56:25.980

0

@user0042 is correct. The best way is to use vectors or another container which removes the need for template that you have created.

using namespace std;
typedef std::vector<std::vector<double>> Double2D;
void printMatrix(Double2D& matrix)
{
    for(int i=0;i<matrix.size();i++)
    {
        for(int j=0;j<matrix[i].size();j++)
        {
             cout<<matrix[i][j]<<" ";
        }
        cout<<endl;
    }
}

int main()
{
    Double2D matrix = { { } }; // fill the matrix here. depending on the compiler you use, you have to use different methods
    printMatrix(matrix);
    return 0;
}

edited Jul 22 '17 at 15:56

answered Jul 20 '17 at 17:36

Sam

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Using your code, I get two errors: 'vector' in namespace 'std' does not name a template type 'printMatrix' was not declared in this scope Any thoughts? – LampPost Jul 20 '17 at 19:19
@LampPost Sorry, the `typedef` above definition of `printMatrix` is missing the ending semicolon. I just edited the post to fix that. – Sam Jul 21 '17 at 20:02

How to send a 2D array to a function?

3 Answers3