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c++rvalue-reference

The compiler doesn't complain when vector<char>&& is bound to vector<char>&

I'm using Visual Studio 2013 Express.

class B{
public:
    vector<char>& a;
    int& b;
    B(vector<char>& i,int& c) :a(i),b(c) {}
};

int main(){
    int l=3;
    vector<char> h;
    shared_ptr<B> bb (new B(std::move(h),l));
    return 0;
}

Why can the code be accepted?When I changed the argument l to std::move(l),the compiler will complain "cannot convert argument 2 from 'int' to 'int &'".

Solution

  • This is a language extension available in the Visual C++ compiler and has existed for quite some time now. The extension allows you to bind an rvalue (tempoarary) to a non-const reference and extend the lifetime of value as if you were binding to a const reference.. If you enable warning level 4 or explicitly enable warning C4239 the compiler will alert you any time the extension is used.

    The documentation for C4239 includes an example that is similar to what's in your question.