问题描述
我阅读了以下链接：-
I read following links :-
我有一个问题我想澄清。
I have some question which i want to clarify.
1）给定POD类，例如：-
1) Given a POD class , say :-
class A{
int val;
};
如果我创建类型A的对象。
If i create an object of type A.
A obj; //将调用由编译器提供的隐式定义的构造函数吗？
现在据我所知，在这种情况下未调用构造函数。
A obj; // will this call implicitly defined constructor provided by compiler ?
Now as far as my understanding in this case constructor is not called.is it correct?
新A（）; //值初始化A，这是零初始化，因为它是POD。
现在在这种情况下，将由编译器提供隐式定义的构造函数吗？
new A(); // value-initialize A, which is zero-initialization since it's a POD.Now in this case will implicitly defined constructor provided by compiler ? Is there is any role of constructor for zero initializing the object?
如果我的理解是错误的，请给我一个示例，其中不调用隐式定义的构造函数吗？全部。
If my understanding is wrong , could you please give me an example where implicitly defined defined constructor is not called at all.
谢谢。
推荐答案
1）正确。 obj.val 未初始化。
1) Correct. obj.val is not initialized.
2）这是一个函数声明，而不是初始化：
2) This is a function declaration, not an initialization:
A obj(); // function obj() returning an A
如果这样做，
A obj{}; //C++11
A obj = A(); // C++03 and C++11
obj 将被值初始化， obj.val 也将被初始化。反过来，这意味着 obj.val 将被零初始化（（ value-initialization 意味着 zero-初始化（针对内置类型）。
obj would be value-initialized, and so would obj.val. This in turn means that obj.val would be zero-initialized (value-initialization means zero-initialization for built-in types).
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