strange behavior of returning a vector

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?

+1 for a complete example & well-composed question.

John Dibling
– John Dibling

2012-05-04 15:23:49 +00:00
Commented May 4, 2012 at 15:23 — John Dibling
– John Dibling, Commented May 4, 2012 at 15:23

JoeG · Accepted Answer · 2012-05-04 13:59:59Z

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;

With debugging versions of the library, this should have crashed.

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