How Can Operator Overloading for Multiple Arguments Be Fixed in C++?

[waht]

I've got an overloaded operator +

newtype X, Y, Z, W;W = X + Y;  // works fine

W = Y + X; // works fine

// but with more arguments I'm getting compiler error

// saying there is no match for operator+

W = X + Y + Z;

Sample code

newtype operator+(newtype &A, newtype &B)
{

newtype C;

//more code

return C;

}

Is there something missing?

 

[Hurkyl]

Just eyeballing it, I agree with the compiler.

Temporary objects cannot be implicitly converted to modifiable references -- the standard doesn't allow it, and even if it did, you shouldn't do it anyways because it can lead to all sorts of really, really hard to debug problems.

Since X+Y is a temporary value, it cannot be converted into the modifiable reference required by your operator+.


Now, the fix is actually very easy: write operator+ correctly! The arguments almost certainly should not be modifiable references -- they should be const references.

(Well, technically there are occasions where you're better off without using references at all)

 

[CFDFEAGURU]

Not sure what you are doing but my code compilies fine. I am using 2008 C++ Express edition.

Here is my code.

#include<cmath>
#include<iomanip>
#include<iostream>

int x,y,z,w,pause;  // needed variables

using namespace std;

int main()
{
	x = 1;
	y = 2;
	z = 3;

	w = x+y;
	w = y+x;
	w = x+y+z;

	cout << w << endl;
	cin >> pause; // dummy input to keep the output screen visible


	return 0;
}

Thanks
Matt

 

[D H]

Even if "your code compiles fine" does not mean it is right. Besides, per your first post, your code does not compile fine. It doesn't even compile, period. I would not call that "fine".

Make the arguments to newtype operator+ be const references and then it will be fine.

 

[CFDFEAGURU]

Yes, const is a must in C++.

Thanks
Matt

 

[waht]

Woe is me. Const ref works like a charm.