Quick question regarding overloading operators

Code:

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// vectors: overloading operators example
#include <iostream>
using namespace std;


class CVector {
  public:
    int x,y;
    CVector () {};
    CVector (int,int);
    CVector operator + (CVector);
};


CVector::CVector (int a, int b) {
  x = a;
  y = b;
}


CVector CVector::operator+ (CVector param) {
  CVector temp;
  temp.x = x + param.x;
  temp.y = y + param.y;
  return (temp);
}


int main () {
  CVector a (3,1);
  CVector b (1,2);
  CVector c;
  c = a + b;
  cout << c.x << "," << c.y;
  return 0;
}

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In the example above, on line #28, the object c is created. And c, without being assigned anything specific, can already use the defined overloaded operator function for the plus sign. How did the computer know to use the overloaded function for the object c? Does it check the class for any overloaded operators to see if it should use that by default instead of the normal operator for the plus sign?

If you look carefully you will discover that CVector has a default constructor on line 9, so there is no real language reason why you couldn't use it in a statement such as c = a + b. In the future you might not want to define member functions inside of the class definition.

It works because the changes are made to a copy of a, which is assigned to c.

Quote:

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Originally Posted by Justin H

How did the computer know to use the overloaded function for the object c? Does it check the class for any overloaded operators to see if it should use that by default instead of the normal operator for the plus sign?

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Essentially, yes.

Quote:

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Originally Posted by whiteflags

It works because the changes are made to a copy of a, which is assigned to c.

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Huh, that's not what the code does. Neither a, nor the pass-by-value copy of a is modified.
Perhaps the code was modified after you saw it? Afterall, line #28 has nothing on it.

Quote:

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Originally Posted by iMalc

Huh, that's not what the code does. Neither a, nor the pass-by-value copy of a is modified.
Perhaps the code was modified after you saw it? Afterall, line #28 has nothing on it.

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I didn't say anything about line 28, but it appears that my actual references are useless anyway. No idea why, I'm comfortable with blaming myself.

Also, I explained this part pretty poorly I admit.
temp.x = x + param.x;
temp.y = y + param.y;

So poorly it was wrong. I didn't bother fixing it because I didn't think it mattered.

SourceForge.net: Do not remove parameter names - cpwiki