c++ - 使用 {0} 初始化结构

Question

我正在调试一些与此基本相同的代码:

struct Foo { int a; int b; };
struct Bar { Bar() {} Foo foo{0}; };

当我创建 Bar 的实例时，好像都是a和 b初始化为零。这是有保证的吗？我在哪里可以在规范中找到它？

Answer 1

根据 cppreference.com

If the number of initializer clauses is less than the number of members [and bases (since C++17)] or initializer list is completely empty, the remaining members [and bases (since C++17)] are initialized [by their default member initializers, if provided in the class definition, and otherwise (since C++14)] by empty lists, in accordance with the usual list-initialization rules (which performs value-initialization for non-class types and non-aggregate classes with default constructors, and aggregate initialization for aggregates). If a member of a reference type is one of these remaining members, the program is ill-formed.

Foo没有默认成员初始值设定项( int b{0}; )，所以 b将通过带有空列表的列表初始化进行初始化，这意味着非类类型的值初始化:b = int() // = 0 .