错误 C2677：二进制“+=”：未找到采用“电影”类型的全局运算符（或没有可接受的转换）

Question

I'm trying to create a generic class which stores Movie objects in an array. I want to override the += and -= operators in order to add or delete an element from the array.

template<typename Element>
movieArray<Element>& movieArray<Element>::operator-=(int position)
{
    // some code here...
    return *this;
}

template<typename Element>
void movieArray<Element>::deleteElem(int position)
{
    this->elements -= position;
}

The delete part works as expected. However, when I do the same thing for the Add operation:

template<typename Element>
movieArray<Element>& movieArray<Element>::operator+=(const Element &elem)
{
    elements[lenght++] = elem;
    return *this;
}

template<typename Element>
void movieArray<Element>::addElem(const Element &elem)
{
    resizeArray();
    this->elements += elem;
}

I receive the following error:

error C2677: binary '+=' : no global operator found which takes type 'Movie' (or there is no acceptable conversion)

I am not sure why this is happening.

If I change Element to int , like I have at the -= method, the code is compiled.

Answer 1

Try this instead:

template<typename Element>
movieArray<Element>& movieArray<Element>::operator-=(int position)
{
    // some code here...
    return *this;
}

template<typename Element>
void movieArray<Element>::deleteElem(int position)
{
    *this -= position;
}

template<typename Element>
movieArray<Element>& movieArray<Element>::operator+=(const Element &elem)
{
    resizeArray();
    elements[lenght++] = elem;
    return *this;
}

template<typename Element>
void movieArray<Element>::addElem(const Element &elem)
{
    *this += elem;
}

Or this:

template<typename Element>
movieArray<Element>& movieArray<Element>::operator-=(int position)
{
    deleteElem(position);
}

template<typename Element>
void movieArray<Element>::deleteElem(int position)
{
    // some code here...
}

template<typename Element>
movieArray<Element>& movieArray<Element>::operator+=(const Element &elem)
{
    addElem(elem);
    return *this;
}

template<typename Element>
void movieArray<Element>::addElem(const Element &elem)
{
    resizeArray();
    elements[lenght++] = elem;
}

Answer 2

We are guessing a lot since you only posted a little fraction of your code. But perhaps you meant:

*this += elem;

which would call your class's overloaded operator+= function that you showed, instead of:

this->elements += elem;

which would call += on the member variable elements . You haven't told us what elements is , but (based on your symptoms) perhaps it has some type which has += defined for int but not for Element .

---

NB. Not related to your compilation error, but resizeArray(); should be inside operator+= , otherwise (assuming that this function is necessary to make space in the array) you will overflow your space when someone calls operator+= instead of addElem .