我怎样才能重载<<运算符

Question

I have to create a Matrix class, and I got some problem to overload the operators

I would like to fill up a matrices using the << operator

Matrix<double> u3(2,2);

u3 << 3.3, 4, 3, 6;


template<class T>
Matrix<T> Matrix<T>::operator <<(T in){
    //Fill up the matrix, m[0] = 3.3, m[1]=4...
    return *this;
}

How overload this operator?

Answer 1

Here's an approach using commas:

#include <iostream>
using namespace std;

struct Matrix {

    struct Adder {
        Matrix& m;
        int index;

        Adder(Matrix& m) : m(m), index(1) {}

        Adder& operator,(float value) {
            m.set(index++, value);
            return *this;
        }    
    };

    void set(int index, float value) {
        // Assign value to position `index` here.
        // I'm just printing stuff to show you what would happen...
        cout << "Matrix[" << index << "] = " << value << endl;
    }

    Adder operator<<(float value) {
        set(0, value);
        return Adder(*this);
    }

};

Demo: http://ideone.com/W75LaH

Some explanations:

The syntax matrix << 5, 10, 15, 20 is achieved in two steps:

• matrix << 5 is evaluated first; it sets the first element to 5 and returns a temporary Adder object that handles further insertions (remembering the index for the next insert)
• Adder has overloaded operator, that performs the following inserts after each comma.

Answer 2

An approach like this would work:

#include <iostream>


template <typename T>
class Mat {
public:
  T val; 
};

template <typename T>
Mat<T>& operator<<(Mat<T>& v, T in) {
  std::cout << in << " ";
  return v;
}

int main() {
  Mat<int> m;
  m << 1 << 2 << 3;
}

Note that I am using a free operator<< function, and do not use commas between the values.