C++ 'typedef' vs. 'using … = …' [duplicate]

问题

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Closed 7 years ago.

Possible Duplicate:
What are the differences between typedef and using in C++11?

The following code compiles and runs. My question is what is the difference between the "typedef" and "using" method for renaming the template specialization?

template<typename T>
struct myTempl{
    T val;
};

int main (int, char const *[])
{
    using templ_i = myTempl<int>;
    templ_i i;
    i.val=4;

    typedef myTempl<float> templ_f;
    templ_f f;
    f.val=5.3;

    return 0;
}

Edit:

If there is no difference, which one would you prefer? / Why was the using ... = ... version introduced?

回答1:

They are the same.

To quote the C++11 standard (or the draft to be specific):

A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that typedef-name. It has the same semantics as if it were introduced by the typedef specifier. In particular, it does not define a new type and it shall not appear in the type-id.

I think the "the same semantics as the typedef specifier" say it all.

来源：https://stackoverflow.com/questions/11224336/c-typedef-vs-using