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Cannot convert parameter 1 from 'std :: _ Vector_iterator <_Myvec>' to 'std :: _ Vector_iterator <_Myvec>'

I have a question that is a little difficult to describe, so please be calm.

I have two classes, A and B, class A has a private member vector:

class A
{
private:
    struct complex
    {
       int x;
       vector< int > y;
    };

    vector< complex > m_resultVector; // <---- the private member

public:
    void getPointerToVector( vector< complex >::iterator it )
    {
        it = m_resultVector.begin();
    }
};

I need to access (read only) from class B, to this m_resultVector;

, I could write a function get

, but it m_resultVector

's a very long vector and I don't want to copy the whole vector to a new one, I want to send its pointer. also the important part - I need class B which cannot change the contentm_resultVector 

class B
{
    struct complex
    {
        int x;
        vector< int > y;
    };

    void functionOf_B()
    {
        A class_A;
        vector< complex >::iterator p_resultVector;

        class_A.getPointerToVector(p_resultVector); // <------ compilation error here

        // some reading from the content of p_resultVector
    }
};

when i try to compile it i get an error:

cannot convert parameter 1 from 'std :: _ Vector_iterator <_Myvec>' to 'Std :: _ Vector_iterator <_Myvec>'

so basically, I have questions -

  • Why am I getting this error? structure is complex

    defined in both classes.
  • where and how do I need to declare on const iterator

    in class B so it will be read-only? I'm not sure...
+3


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2 answers


This is because A::complex

and B::complex

are different types (with the same content, but that doesn't matter). So vector<A::complex>

and vector<B::complex>

different. Move the definition struct complex

outside A

and B

.

Also there are more problems in your code. A::getPointerToVector

does nothing as it copies the vector input iterator to the temporary one, assigns a value to it and after returning from this function, all is lost. Using this approach, you need to pass vector<complex>::iterator

as a reference (thus vector<complex>::iterator&

).

I would rather write a method in A

like this



const vector<complex>& get_vector() const
{
    return m_resultVector;
}

I am so, you can do it.

void foo()
{
    A class_A;
    // do something with A
    const vector<complex>& p_result = class_A.get_vector();

    // now you are holding whole vector and you can call methods
    // defined as const (which does not modify that vector)
    p_result.begin();
    p_result.at(0);
    p_result.end();
}
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Zereges' solution seems to be good. But I understand that you don't want to return a vector. I couldn't find a solution other than below.

In class A:

void getPointerToVector(int position, int &var,vector<int>& o_Vec)
{

    vector<complex>::iterator itr;
    complex c;
    c = m_resultVector.at(position);
    var = c.x;
    o_Vec = c.y;

}


In class B:

 void functionOf_B()
{

    A class_A;
    int aVar;
    std::vector<int> vec;
    class_A.getPointerToVector(2, aVar, vec);


        // some reading from the content of p_resultVector

}

I'm not sure how efficient and difficult it is. I would suggest using Zereges' solution better

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