I try to overload operator << and ++ (post and pre). This is part of my code, but I get error "e0349: no operator matches these operands". Could you tell me where I made a mistake? (C++, VS2022)
#include <iostream>
#include <string>
using namespace std;
class K {
int x, y;
public:
K(int a, int b) :x(a), y(b) {};
K() :x(0), y(0) {};
K operator++(int);
K& operator++();
friend ostream& operator<< (ostream & str, K & obj);
};
K K::operator++(int) {
K temp(*this);
x += 1;
y += 1;
return temp;
}
K& K::operator++() {
x += 1;
y += 1;
return *this;
}
ostream& operator<<(ostream& str, K& obj) {
str << "[" << obj.x << ", " << obj.y << "]";
return str;
}
int main(int argc, char* argv[])
{
K obj{10, 20};
cout << obj++ << endl; //here I get error
cout << obj << endl;
cout << ++obj << endl;
}
Simply the post-operator++ is written so that it returns a copy of the temporary value which can be used as rvalue but being that the signature of the insertion operator requires a reference of the value, it does not know how to retrieve the data passed as a copy. This is how you should modify the overloading function of the extract operator:
ostream& operator<<(ostream& str, K const& obj) {
str << "[" << obj.x << ", " << obj.y << "]";
return str;
}
You're simply telling the function that the passed value will have a constant reference that it won't change over time. So it is as if you are taking the reference of the copy value. I know it's very tricky as a thing but I should have cleared your minds enough
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