在哪些情况下根本没有构造函数，甚至没有默认构造函数? [英] In which cases there is no constructor at all, even a default constructor?

问题描述

在这本书中，我目前正在阅读我遇到的这本书:

In this book I am currently reading I ran across this:

一个类不需要构造函数.如果对象不需要初始化，则不需要默认的构造函数.

A class doesn't need a constructor. A default constructor is not needed if the object doesn't need initialization.

从上述推断，我是否正确，在某些情况下编译器不会为类/结构生成默认构造函数?如果是，那是什么情况?我敢说POD可能就是其中之一.还有其他吗?

Am I correct in inferring from the above that the compiler does not generate a default constructor for the class/structure in some cases? If yes, what are those cases? I will venture and say POD is probably one. Are there any other?

我已经更改了标题，因为原始标题的含义是我询问何时未定义默认构造函数，而不是询问何时类根本没有构造函数.

I have changed the title as the original title gave the meaning that I asked when was a default constructor not defined instead of asking when does a class not have a constructor at all.

推荐答案

一个类不需要构造函数.如果对象不需要初始化，则不需要默认的构造函数.

A class doesn't need a constructor. A default constructor is not needed if the object doesn't need initialization.

我认为作者正在谈论这种情况:

I think the author is talking about this situation:

some_type some_function () {
   POD_type this_is_intentionally_uninitialized;
   ...
}

在某些情况下，不会调用构造函数，句号.一旦您编写了构造函数，便没有POD类，因此现在将调用该构造函数.

Under some circumstances a constructor won't be called, period. As soon as you write a constructor you don't have a POD class, so now the constructor will be called.

让一个包含随机未初始化数据的对象运行是好事还是坏事，完全是另一个问题.

Whether it is a good or bad thing to have an object running around that contains random, uninitialized data is a different question entirely.

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