c++ - 语法理解问题

Question

请帮助我理解 main 函数中的行。这是什么意思

#include<iostream>

struct ABC
    {
      private:
       int A,
       float B;

      public :
       ABC() {};
       ~ABC(){};

    };

    int main()
    {
       ABC A={};     // What does this statement means?
      return 0;
    }

Answer 1

ABC A={} 与调用不带参数的构造函数相同。在你的例子中是 ABC A = ABC();

让我们考虑这个类(带有 0/1/2 参数的公共(public)构造函数)

class Hello {
private:
  int x;
  float y;
public:
  Hello() {}
  Hello(int _x) : x(_x) {}
  Hello(int _x, float _y) : x(_x), y(_y) {}
};

Hello h = {} == Hello h = Hello() == 只是 Hello h

Hello h = {1} == Hello h = Hello(1) == Hello h; h.x = 1;

Hello h = {1, 2} == Hello h = Hello(1, 2) == Hello h; h.x = 1; h.y = 2;