Question

I’m doing a homework that needs to be done using templates: it’s a matrix class.

One of tells me to overload the operator ()(int r, int c);, so I can access my data using obj(a, b); or change it with obj(a, b)=100;.

The template for my class is template<class T, int C, int R>;
Then I created inside my class in the public scope a:

T& operator()(int r, int c);//LINE 16

The implementation is simple.

I tried in 2 ways:

template <class T>
T& Matrix::operator()(int r, int c){
    return matrixData[r][c];
}

template <class T, int C, int R>
T& Matrix::operator()(int r, int c){ 
    return matrixData[r][c];
}

In the last one I get the error telling me:

16: Error: expected type-specifier before '(' token

the line 16 is above with a commentary error:

no 'T& Matrix<T, C, R>::operator()(int, int)' member function declared in class 'Matrix<T, C, R>'

Answer 1

The class is template<class T, int C, int R> class Matrix {...}:

The following works for me:

#include <iostream>

template<typename T, int R, int C>
class Matrix {
  T data[R][C];
public:
  T& operator()(int r, int c);
};

template <typename T, int R, int C>
T& Matrix<T, R, C>::operator()(int r, int c) {
  return data[r][c];
}

int main() {
  Matrix<int, 3, 4> m;
  m(0, 1) = 42;
  std::cout << m(0, 1) << std::endl;
}