Garbage appears in vector after inserting result of operator

Question

I have an object with an operator defined like this: ``` P& operator +(const P &rhs) { return P(x + rhs.x, y + rhs.y, z + rhs.z); } ``` It does not have custom copy or assignment operators. After I assign directly the result of an addition inside the vector, garbage appears inside it. ``` P p1(1.0, 0.0, 0.0); P p2(0.0, 0.0, 0.0); vector

v(1); v[0] = p1 + p2; // v[0] now contains garbage. ``` If I do it through a variable, everything is as expected. ``` vector

u(1); P q = p1 + p2; u[0] = q; // u[0] contains correct value. ``` What can be the reason for such behavior? What is the difference between the two cases?

Accepted Answer

You return a reference to a temporary. This is a bad idea, since the temporary goes out of scope at the end of the function (in this case, the `operator+` function). Declare your operator as:

```
P operator +(const P &rhs) const
```

instead.

Garbage appears in vector after inserting result of operator

Solution

Problem