Passing 2d array c++

Question

I'm trying to make a small program that swaps two columns and I have to use functions in order to do that but I just started on c++ and I cant get what I do wrong.

#include <iostream> using namespace std; int colSwap(int ng, int ns, int pin[][ns]) { for (int i = 0; i < 3; ++i) { for (int j = 0; j < 4; ++j) { cout << " i:" << i << " j:" << j << " " << pin[i][j] << " " << endl; } cout << endl; } } int main() { int ng = 3; int ns = 4; int pin[3][ns] = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}}; colSwap(ng,ns,pin); return 0; }

I know that write it this way

int colSwap(int pin[][4]) { }

but i need another method

You cannot reference another parameter to determine the size. Write int colSwap(int ng, int ns, int** pin) { instead. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented May 23, 2016 at 14:43
@πάνταῥεῖ Except that an array of arrays is really not the same as a point to pointer. — Some programmer dude
– Some programmer dude, Commented May 23, 2016 at 14:45

Some programmer dude · Accepted Answer · 2016-05-23 14:43:33Z

While it's possible to pass the sizes like that in C, it's not possible in C++. The reason being that C++ doesn't have variable-length arrays. Arrays in C++ must have its size fixed at the time of compilation. And no, making the size arguments const does not make them compile-time constants.

I recommend you use std::array (or possible std::vector) instead.

AlphaRL · Accepted Answer · 2016-05-23 14:56:22Z

You can use template function

#include <iostream> using namespace std; template <size_t R, size_t C> void colSwap(int(&arr)[R][C]) { for (int i = 0; i < R; ++i) { for (int j = 0; j < C; ++j) { cout << " i:" << i << " j:" << j << " " << arr[i][j] << " " << endl; } cout << endl; } } int main() { const int ng = 3; const int ns = 4; int pin[ng][ns] = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}}; colSwap(pin); return 0; }

When declare an array, its size must be fixed, so ng and ns should be const int. The type of pin is actually int[3][4], you can just pass a reference of this type and let compiler deduce the size.

Collectives™ on Stack Overflow

Passing 2d array c++

2 Answers 2

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Linked

Related