在构造函数中调用方法

发布于 2024-10-15 18:59:13 字数 1184 浏览 4 评论 0原文

Herb Sutter 在他的一篇 http://www.gotw.ca 文章中提到构造了一个对象（具有有效的仅当构造函数执行completes.ie时，以粗略的方式将其控制超出其最后的大括号。

现在考虑下面的代码

class A
{
  public:
  A() 
  { 
      f();
  }

  void f() 
  { 
      cout << "hello, world"; 
  }

}; 

int main()
{
   A a;
}

现在根据 Herb 的说法，我们不能说，由于 A 尚未在其构造函数内完全构造，因此在构造函数内调用 f() 是无效的，因为“this”ptr 尚未准备好。

构造函数内确实有一个有效的“this”，并且 f() 确实被调用。

我不认为赫伯说了什么不正确的事情……但我猜我的解释不正确……有人可以向我解释一下那到底是什么吗？

以下是文章的链接：http://www.gotw.ca/gotw/066.htm 它讨论了构造函数的异常。具体来说，这是我的问题所基于的摘录：

- 对象的生命周期何时开始？ 当其构造函数成功完成并正常返回时。也就是说，控制到达构造函数主体的末尾或较早的 return 语句。

- 对象的生命周期什么时候结束？当它的析构函数开始时。也就是说，控制到达析构函数体的开头。 这里重要的一点是，对象在其生命周期开始之前的状态与其生命周期结束之后的状态完全相同 - 没有对象，期间。这一观察给我们带来了关键问题：

我们可以将 C++ 构造函数模型总结如下：

Either:

(a) The constructor returns normally by reaching its end or a return statement, and the object exists.

Or:

(b) The constructor exits by emitting an exception, and the object not only does not now exist, but never existed.

原文

Herb Sutter mentions in one of his http://www.gotw.ca articles that an object is constructed(has valid existence) only if the constructor executes completes.ie to put it in a crude way control passes beyond its final brace.

Now consider the following code

class A
{
  public:
  A() 
  { 
      f();
  }

  void f() 
  { 
      cout << "hello, world"; 
  }

}; 

int main()
{
   A a;
}

Now from what Herb says, can't we say that since A is not completely constructed inside its constructor Calling f() inside the constructor is invalid as the "this" ptr is not ready yet.

Still there is indeed a valid "this" inside the constructor and f() does get called.

I don't think Herb is saying something incorrect... but guess i am interpreting it incorrectly....can some explain to me what exactly that is?

Here is the link to the article : http://www.gotw.ca/gotw/066.htm
It talks about exceptions from constructors. Specifically here is the extract from it on which my question is based:

-When does an object's lifetime begin?
When its constructor completes successfully and returns normally. That is, control reaches the end of the constructor body or an earlier return statement.

-When does an object's lifetime end?
When its destructor begins. That is, control reaches the beginning of the destructor body.
Important point here is that the state of the object before its lifetime begins is exactly the same as after its lifetime ends -- there is no object, period. This observation brings us to the key question:

We might summarize the C++ constructor model as follows:

Either:

(a) The constructor returns normally by reaching its end or a return statement, and the object exists.

Or:

(b) The constructor exits by emitting an exception, and the object not only does not now exist, but never existed.

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