C++11老关键字的新含义(auto, using，extern)

出处:http://blog.csdn.net/cnsword/article/details/8034947

C++11对关键字进行了修订，加入了nullptr、constexpr、decltype、default、static_assert等，同时原有的关键字（auto，using，extern）含义和用途进行了修订。在这里主要了解一下对auto、using、extern这三个关键字的修订。

auto

自动化变量

auto a = 12; auto b = 12.0f; auto c = true; auto d = [] (int x)->int{ return 12;}; auto e = std::bind(&func, _1);

延迟绑定

template<typename T, typename L> auto fun(T x, L y)->decltype(x + y){return x;}

using

定义别名

template<typename T> using Tlist = std::list<T>; using Tlist = std::list<char>; using df = void(*)();//等价于typedef void(*df)() 和typedef的区别: 定义一般类型的别名没区别。C++11标准7.1.3.2：( https://isocpp.org/files/papers/N3690.pdf ) 2 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. [Example: using handler_t = void (*)(int); extern handler_t ignore; extern void (*ignore)(int); // redeclare ignore using cell = pair<void*, cell*>; // ill-formed — end example ] 定义模板的别名，只能使用using。

使用外部构造

using A::A;

引入外部类型

using typename A;

extern

外部模板

extern template<typename T>void(T t);