Overload operator [] to replace vector elements

Question

I have a classA which has a vector< classB* > vObject.

class ClassA{
public:
     ClassB** operator [] (int index);
private:
     vector<ClassB*> vObject
};

Let's Assume that vObject is filled with some classB* objects. What I want to do is to be able to replace classB* elements of vector like that:

classA_obj[3] = classA_obj[5];
classA_obj[1] = classB_obj;

I tried to return a pointer of ClassB Element. Here is my current operator implementation:

ClassB** ClassA::operator [](int index){
    return &vObject[index]; }

After that i tried the following:

*classA_obj[3] = *classA_obj[5]

The code of doing all the work with just a vector would be:

vector<ClassB*> vObject;
vObject.push_back(new ClassB(ARG1,ARG2));
vObject.push_back(new ClassB(ARG1,ARG2));
vObject[0] = vObject[1];

I'm really confused about this, I thought my code was right but it actually doesn't work. I would love if someone could tell me what I'm doing wrong.

The above code is just a sample of my actual code.

score 2 · Accepted Answer · edited May 23 '17 at 11:48

If you return a reference, you will be able to do the replacement you requested.

class ClassA{
public:
     ClassB*& operator [] (int index) { return vObject[index]; }
private:
     std::vector<ClassB*> vObject
};

However, the way you have described your usage seems to indicate you can easily change your vector to hold ClassB objects instead of pointers.

class ClassA{
public:
     ClassB& operator [] (int index) { return vObject[index]; }
private:
     std::vector<ClassB> vObject
};

Then instead of pushing new ClassB into the vector, you just push ClassB:

vObject.push_back(ClassB(ARG1,ARG2));
vObject.push_back(ClassB(ARG1,ARG2));

This has the advantage you not needing to explicitly visit your container to delete the pointers. Otherwise, you will need to update ClassA to obey the rule of three.

Thanks, changing ClassB** to ClassB*& worked. My whole application depends on ClassB with pointer and I made some code to delete the pointers in the vector, so I will stick with that but thanks for the info. — George Sofianos, Aug 09 '12 at 14:22

score 0 · Answer 2 · answered Aug 09 '12 at 14:01

0

The ordinary std::vector returns a reference, so you should probably try that:

ClassB*& ClassA::operator [](int index)
{
     return vObject[index]; 
}

answered Aug 09 '12 at 14:01

Bo Persson

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Thanks for your answer, I didn't know vector returns a reference :) – George Sofianos Aug 09 '12 at 14:28

score 0 · Answer 3 · answered Aug 09 '12 at 14:03

In the definition:
class A {
  public:
          ClassB*& operator [] (int index) { return vObject.at(index); };
  private:
          vector<ClassB*> vObject;
}

It's a inline function, nothing else to be done. However, I would check index just for sanity.

Overload operator [] to replace vector elements

3 Answers3

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