Passing 2D arrays to functions

[Kalcor]

Can someone show a way to pass a 2D array to a function without knowing both of the dimensions? And explaining why please <3

[Cubbi]

Array size is part of array type, so to pass it to a function, you have to know the sizes at compile time. E.g. you can pass int[2][2] into a function taking int (&a)[2][2]:

#include <iostream>

void print2x2(const int (&a)[2][2]) {
   std::cout << a[0][0] << a[0][1] << '\n'
             << a[1][0] << a[1][1] << '\n';
}

int main() {
    int a2[2][2] = {{1,2}, {3,4}};
    print2x2(a2);
}

demo: http://coliru.stacked-crooked.com/a/14f8fe1d6675fdfb

To make it possible to call it if you don't know the sizes, you can parametrize that function:

#include <iostream>

template<class T, std::size_t R, std::size_t C>
void print2D(const T(&a)[R][C]) {
   for(const auto& row: a) {
     for(const auto& n: row) {
        std::cout << n << ' ';
     }
     std::cout << '\n';
   }
}

int main() {
    int a1[2][3] = {{1,2,3}, {4,5,6}};
    print2D(a1);
    int a2[2][2] = {{1,2}, {3,4}};
    print2D(a2);
}

demo http://coliru.stacked-crooked.com/a/2e519a4515af4a51

If that seems complex, you're right. It's generally much better to use std::array or, if you don't know sizes until run time, std::vector:

void print2D(const std::vector<std::vector<int>>& a) {
// same code
}
int main() {
    std::vector<std::vector<int>> a1 = {{1,2,3}, {4,5,6}};
    print2D(a1);
    std::vector<std::vector<int>> a2 = {{1,2}, {3,4}};
    print2D(a2);
}

demo: http://coliru.stacked-crooked.com/a/56cfee1705c86a09