使用 {} 初始化 class 成员

Question

Someone gave me (part of) the following code:

struct MyStruct
{
    int x = {};
    int y = {};

};

I never saw this syntax before, what does initialization with {} mean?

Answer 1

This is default member initializer (since C++11),

Through a default member initializer, which is a brace or equals initializer included in the member declaration and is used if the member is omitted from the member initializer list of a constructor.

The initialization itself is copy-list-initialization (since C++11), as the effect, the data member x and y would be value-initialized (and zero-initialized as built-in type) to 0 .

Answer 2

Since the C++11 standard there are two ways to initialize member variables:

1. Using the constructor initialization list as "usual":

    struct Foo { int x; Foo(): x(0) { } };

2. Use the new inline initialization where members are getting their "default" values using normal initialization syntax:

    struct Foo { int x = 0; };

Both these ways are for many values and types equivalent.