Why are std::begin and std::end “not memory safe”?

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Category:Languages

In this blog post, Eric Niebler states that:

What is wrong with std::begin and std::end? Surprise! they are not memory safe. Consider what this code does:

extern std::vector<int> get_data(); auto it = std::begin(get_data()); int i = *it; // BOOM 

std::begin has two overloads for const and non-const lvalues. Trouble is, rvalues bind to const lvalue references, leading to the dangling iterator it above.

I'm having trouble understanding his point and why it is a dangling reference. Could someone explain?

 


The get_data function returns an object. When used the way shown, that object will be a temporary object, which will be destructed once the full expression ends. The iterator now references a vector object which no longer exists, and can't be dereferenced or used in any useful way.

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