<< Operator overloading error in C++ -

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i'm c++ beginner, trying learn online videos. in of operator overloading examples in lectures following code there , gives error 

 error: no match 'operator<<' in 'std::cout << operator+(((point&)(& p1)), ((point&)(& p2)))'compilation terminated due -wfatal-errors.

on line marked comment. can please tell what's wrong in code? trying professor explained in lecture can't compile.

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#include <iostream> using namespace std;   class point{ public:     double x,y; };  point operator+ (point& p1, point& p2) {     point sum = {p1.x + p2.x, p1.y + p2.y};     return sum; }  ostream& operator<< (ostream& out, point& p) {     out << "("<<p.x<<","<<p.y<<")";     return out; }   int main(int argc, const char * argv[]) {     point p1 = {2,3};     point p2 = {2,3};     point p3;     cout << p1 << p2;      cout << p1+p2; // gives compliation error     return 0; }

it's problem const correctness. operator+ returns temporary, can't bind non-const reference when calling operator<<. make signature:

ostream& operator<< (ostream& out, const point& p)

while don't need fix compilation error, won't able add const points unless fix operator+ similarly:

point operator+(const point& p1, const point& p2)

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