• 对于定义一般类型的别名，二者没有区别。
  • 对于定义模板的别名，只能用using。(c++11 还是鼓励用using)
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#include <iostream>

template <typename T>
class A
{
public:
    A() { std::cout << "A " << typeid(T).name() << std::endl; }
};

template <typename T>
using B = A<T>;

template <typename T>
typedef A<T> C;

int main()
{
    A<int> a;
    B<int> b; // OK, B is an alias of class A.
    C<int> c; // Syntax Error, C cannot be recognized as a type.
    return 0;
}