Question

I’m having a trouble overloading operator [] for both read and write in my objects. This is a large code with different components and I’m not going to put all the details here since it wont help. In a nutshell what I have is the following

class MyObject(){
    inline SetterProxy& operator[](int i) {
        SetterProxy a(i);
        return a;
    }
    inline double operator[](int i) const{            
        return some_value;
    }
}

The first overloaded [] works fine for assigning values (if you are wondering what the SetterProxy is, I have to use Proxy classes to be able to do some checking and internal function calls before assigning values). However, the second one which should supposedly be called when reading does not work and the code crashes. I’m not sure what is happening here but when I comment out the first one it just works fine! Could it be that compiler somehow confuses the two since they are both inline?

Any thought would be appreciated.

EDIT:
Ok here is the SetterProxy itself:

class SetterProxy{
private:
    Vec v;
    int i;
    double *ptr_val;
public:
    inline SetterProxy(Vec v_, int i_) {
        v = v_;
        i = i_;
        VecGetArray(v,&ptr_val);
    }
    inline ~SetterProxy(){
        VecRestoreArray(v,&ptr_val);
    }

    inline void operator=(double rhs ){
        ptr_val[i] = rhs;
    }
};

Although I dont think its coming directly from that. Also initially I had it to return by value and I though changing it to reference would be more efficient. I think this should be safe since the assignment is done in the Proxy operator=() class and after that the proxy class goes out of scope. Either way, that does not save my problem!

Answer 1

You’re returning a reference to a local variable – it goes out of scope when the operator returns, leaving your reference dangling. A good compiler should warn you about this if you turn the warning setting up to a reasonable level.