c++ - C ++ 11中的'typedef'和'using'有什么区别？(What is the difference between 'typedef' and 'using' in C++11?)

Question

I know that in C++11 we can now use using to write type alias, like typedef s:

(我知道在C ++ 11中，我们现在可以使用using来编写类型别名，例如typedef ：)

typedef int MyInt;

Is, from what I understand, equivalent to:

(据我了解，相当于：)

using MyInt = int;

And that new syntax emerged from the effort to have a way to express " template typedef ":

(并且，这种新语法是通过努力表达“ template typedef ”的方式而出现的：)

template< class T > using MyType = AnotherType< T, MyAllocatorType >;

But, with the first two non-template examples, are there any other subtle differences in the standard?

(但是，对于前两个非模板示例，标准中是否还有其他细微差别？)

For example, typedef s do aliasing in a "weak" way.

(例如， typedef会以“弱”方式进行别名。)

That is it does not create a new type but only a new name (conversions are implicit between those names).

(也就是说，它不会创建新的类型，而只会创建一个新名称（这些名称之间的转换是隐式的）。)

Is it the same with using or does it generate a new type?

(是否与using相同或会生成新类型？)

Are there any differences?

(有什么区别吗？)

  ask by Klaim translate from so

Answer 1

They are equivalent, from the standard (emphasis mine) (7.1.3.2):

(它们与标准（强调我的）（7.1.3.2）是等效的：)

A typedef-name can also be introduced by an alias-declaration.

(typedef名称也可以通过别名声明来引入。)

The identifier following the using keyword becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that typedef-name.

(using关键字后面的标识符变为typedef名称，而标识符后面的可选attribute-specifier-seq属于该typedef名称。)

It has the same semantics as if it were introduced by the typedef specifier.

(它具有与typedef说明符引入的语义相同的语义。)

In particular, it does not define a new type and it shall not appear in the type-id.

(特别是，它没有定义新的类型，也不应出现在type-id中。)