Question

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How come a non-const reference cannot bind to a temporary object?

This program:

int fun()
{
    return 1;
}

int main()
{   
    const int& var = fun();

    return 0;
}

My question is why I must put a const befor the var definition? If not ,g++ will give me an error ,goes something like “invalid initialization of non-const reference of type ‘int&’ from a temporary of type ‘int’.”
what is the ‘const’ for ?

Answer 1

In this situation you need const because reference initialization requires a variable with an address, not simply a value. Therefore the compiler must create an anonymous variable which you cannot access other than through the reference; the compiler does not want you to access the variable that you did not declare.

If you would declare the variable explicitly, const would be unnecessary:

int tmp = fun();
int &var(tmp);