自动初始化列表的类型 [英] Type of an auto initialized list

问题描述

在下面的C ++代码中，a的类型是什么? typeid返回St16initializer_listIPKcE

In the C++ code below, what is type of a? typeid returns St16initializer_listIPKcE

auto a = { "lol", "life" };

推荐答案

有空时

auto a = { "lol", "life" };

编译器将尝试推导std::initializer_list，其中类型是所有元素的含义.在这种情况下，"lol"和"life"都是const char[]，所以您有一个std::initializer_list<const char*>.

The compiler will try to deduce a std::initializer_list where the type is what all of the elements are. In this case "lol" and "life" are both a const char[] so you have a std::initializer_list<const char*>.

如果您有类似的东西

auto foo = { 1, 2.0 };

然后，由于元素类型不同，您将遇到编译器错误.

Then you would have a compiler error since the element types are different.

带有一个期望的自动推论器列表的规则如下

The rules for auto deduction of intializer list are as follows with one expection

auto x1 = { 1, 2 }; // decltype(x1) is std::initializer_list<int>
auto x2 = { 1, 2.0 }; // error: cannot deduce element type
auto x3{ 1, 2 }; // error: not a single element
auto x4 = { 3 }; // decltype(x4) is std::initializer_list<int>

期望是在C ++ 17之前

The expection is that before C++17

auto x5{ 3 };

是std::intializer_list<int>，在C ++ 17中，大多数已经采用该规则的编译器都将其推导为int.

is a std::intializer_list<int> where in C++17 and most compilers that already adopted the rule it is deduced as a int.

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