定义类的向量的成员变量的引用

Question

This code explains an example of what I want to do:

class Object
{
public:
    int data;

    Object() : data(0) {}
    Object(int data) : data(data) {}
};

int dataSum(vector<int>& dataReference)
{
    int sum = 0;
    for(int i = 0; i < dataReference.size(); i++)
    {
         sum += dataReference[i];
    }
    return sum;
}

int main()
{
    vector<Object> myObject(5);
    int mySum = dataSum(myObject.data); // this line does not work

    return 0;
}

It's obvius that this can be done easier making dataSum a member function of Object, but this is not what I am asking. How can I just reference myObject.data? Or at least doing the same with a pointer if it cannot be done with a reference.

Edit: Some people have told me that the question is not clear. What I want to do is reference every integer of myObject[i].data putting them in a vector<int> reference. Sorry also If I have put some grammatical error, English is not my native language.

Answer 1

Do you want this?

int dataSum(const vector<Object>& dataReference)
{
  int sum = 0;
  for (int i = 0; i < dataReference.size(); i++)
  {
    sum += dataReference[i].data;
  }
  return sum;
}

int main()
{
  vector<Object> myObject{ 1,2,3,4 };
  int mySum = dataSum(myObject); // mySum will be 1+2+3+4 (=10) here.

  return 0;
}

or better:

int dataSum(const vector<Object>& dataReference)
{
  int sum = 0;
  for (const auto & object : dataReference)
  {
    sum += object.data;
  }
  return sum;
}

Answer 2

Why can't you use std::accumulate ?

vector<Object> myObject(5) { 1, 2, 3, 4, 5 };
int mySum = std::accumulate(myObject.begin(), myObject.end(), 0, 
            [](int init, const Object& obj)
            {
                return init + obj.data;
            }); // mySum = 15

This removes the need for the function in the first place and achieves what you want with a simple function call!

If you wanted to do the same thing with a std::vector<int> , then you could just call the same function without a binary predicate.

Answer 3

You are attempting to pass std::vector<Object>& into a method whose signature requires std::vector<int>& . If you want to handle a vector of Object types then that's what you need to implement. If you want to use the method you have defined for dataSum then you need to use it like this.

std::vector<int> numVec = {1, 2, 3, 4, 5};
Object obj;
int sum = obj.dataSum(numVec);