overloading

[aasaa]

why this code won't work?

#include<iostream>

//=============== Complex ============================
class Complex {

	friend Complex operator +(const double& d, const Complex& z) const;					// return const 

private:
	double _r,_i;

public:
	Complex():_r(0),_i(0){}
	Complex(int r,int i):_r(r),_i(i){}

};

//============== Global Functions ===============================
Complex operator +(const double& d, const Complex& z) const {	// he have access for private parameters because of friend declaration
	return Complex(z._r+d,z._i);
}


// =========================== Main Functions ============================================
void foo(){
	Complex z1(1,1),z2,z3;
	z2 = 1 + z1;							// 1
}
// =========================== Main ============================================
int main(){
	foo();

return 0;
}

while this is working good:

#include<iostream>

//=============== Complex ============================
class Complex {

	friend Complex operator +(const double& d, const Complex& z) ;					// return non const 

private:
	double _r,_i;

public:
	Complex():_r(0),_i(0){}
	Complex(int r,int i):_r(r),_i(i){}

};

//============== Global Functions ===============================
Complex operator +(const double& d, const Complex& z)  {	// he have access for private parameters because of friend declaration
	return Complex(z._r+d,z._i);
}


// =========================== Main Functions ============================================
void foo(){
	Complex z1(1,1),z2,z3;
	z2 = 1 + z1;							// 1
}
// =========================== Main ============================================
int main(){
	foo();

return 0;
}

when I compile the first code I get:
overloading.cpp:6: error: non-member function ‘Complex operator+(const double&, const Complex&)’ cannot have cv-qualifier
overloading.cpp:20: error: non-member function ‘Complex operator+(const double&, const Complex&)’ cannot have cv-qualifier

[Catfish]

const is only for member functions, not global functions.

Your Complex operator +(const double& d, const Complex& z) doesn't need to use const to guarantee that it doesn't change the object it's part of... because it's not part of an object.

[aasaa]

ok got it but does it mean that in global function we can't return const ?
what is the reason behind that that global function does not return const?

thanks;

[Catfish]

const int function1(); // this is how you return a const

int function2() const;
// here const says that function2 cannot change contents of the object it's part of
// function2 must be part of a class, and not be a global function 

You can return a const but it doesn't make sense to do so for local variables inside that function.

[aasaa]

thanks, It seems that today is not my day !!