C ++的"new"运算符是如何实现的 [英] How is the C++ 'new' operator implemented

问题描述

Class B;
B *b  = new B();       // default constructor
B *b1 = new B(10);     // constructor which takes an argument B(int x)

但是，如果我们要编写new的自定义版本，则语法为

However, if we want to write a custom version of new, the syntax is

Class B
{
  /*...*/
  static void* operator new(size_t size);
}

如何将语句new B()转换为的函数调用 operator new(sizeof(B))?

How is the statement new B() converted to a function call for operator new(sizeof(B))?

如何跟踪要调用的构造函数，即如何区分new B()和new B(int x)?

And how does it keep track of which constructor to call i.e. how does it distinguish between new B() and new B(int x)?

new是否在C ++中实现为宏?

Is new implemented as a macro in C++?

推荐答案

您的问题应该是:

当B::operator new语法相同时，编译器如何区分new B()和new B(10)?

How compiler distinguish between new B() and new B(10), when the B::operator new syntax is same ?

好吧，new 只分配内存，然后编译器立即将调用插入构造函数.因此，与调用new B，new B()或new B(10)无关.

Well, new just allocates the memory and immediately after that the compiler inserts the call to the constructor. So it's irrespective if you call new B, new B() or new B(10).

编译器解释如下:

B *b = static_cast<B*>(B::operator new(sizeof(B)))->B();
B *b1 = static_cast<B*>(B::operator new(sizeof(B)))->B(10);

实际上，构造函数不返回任何内容.但是上面的伪代码只是内部内容的类比表示.

In actual a constructor doesn't return anything. But above pseudo code is just an analogical representation of internal stuff.

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