Question

I have the following problem:

#include <vector>
#include <iostream>
using namespace std;


class Mat {
public:

        typedef vector<float>::size_type size_type;

        Mat (size_type k, size_type m)
        :data_(k*m){}

        inline vector<float> data() const {return data_;}

        vector<float> data_;
};

int main(){

    Mat f (6, 10);

    cout << f.data().size() << " " << f.data().end() - f.data().begin();

}

the output is 60 122.

I thought the entire vector data_ is moved over and over again, but why are begin() end() invalid after this operation?

Answer 1

You are creating a temporary copy of the vector every time you call data(). You’re then doing iterator arithmetic on iterators pointing to different copies.

Change the signature of data() to const vector<float>& data()const;