Overload operator () with templates

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>'

NPE · Accepted Answer · 2012-11-26 17:28:00Z

3

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;
}

edited Nov 26, 2012 at 17:28

answered Nov 26, 2012 at 16:56

NPE

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4 Comments

Lefsler Over a year ago

It says: wrong number of parameters. I created some friend operators and they worked well, but now i cant solve that.

NPE Over a year ago

@demonofnight: The code in my (edited) answer compiles fine for me.

Lefsler Over a year ago

If i keeps only the class T it dont work, it seems i need to put the <class T, int R, int C>. It tells me that the number of arguments should be 3 and not 1. The class is template<class T, int C, int R> class Matrix{...} If i fix that with all the 3 parameters, my main tells me that i have a undefined referece to matrix<int, 100, 100>::operator()(int, int)

Lefsler Over a year ago

Thanks, the problem now is, the compiler tells me that i have a undefined reference to matrix<int, 100, 100>::operator()(int, int), so i'm looking if its because of the implementation or if i did something wrong/

Ken Wayne VanderLinde · Accepted Answer · 2012-11-26 16:56:58Z

1

If I understand correctly you're missing the type on Matrix:

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

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

answered Nov 26, 2012 at 16:56

Ken Wayne VanderLinde

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