关于C ++中的新布局 [英] Regarding placement new in C++

问题描述

我在放置新操作符时遇到了问题.我有两个程序:Program1(operator.cpp)和Program2(main.cpp): 程序1:operator.cpp

I am having a problem with the placement new operator. I have two programs: Program1 (operator.cpp) and Program2 (main.cpp): Program1: operator.cpp

void *operator new(size_t size)
 {
   void *p;
   cout << "From normal new" << endl;
   p=malloc(size);
   return p;
 }
 void *operator new(size_t size, int *p) throw()
 {
    cout << "From placement new" << endl;
    return p;
 }

这是第一个链接到的第二个程序: main.cpp:

Here is the second program to which the first is linked: main.cpp:

     #include <new>
      int main()
      {
        int *ptr=new int;
        int *ptr1=new(ptr) int(10);
      }

我正在分别编译operator.cpp和main.cpp，如下所示:

I am individually compiling operator.cpp and main.cpp as shown:

operator.cpp: g++ -g -c -o operator operator.cpp

然后将其与main.cpp链接:

Then linking it with main.cpp:

g++ -g -o target operator main.cpp.

令人惊讶的是，当我执行"./target"时，它正在打印:"From normal new". 预期的输出是:从正常新 从新的展示位置开始.

Surprisingly, when i am executing "./target" it is printing: "From normal new". The expected output is: From normal new From placement new.

但是，如果将新放置位置和主放置位置放置在同一文件本身中，则输出将如预期的那样:来自普通新位置，来自新放置位置

有人可以帮助我吗? 这些东西与我的公务有关，非常紧急.

Can anyone please help me regarding this? This stuff is related to my official work and is very very urgent.

推荐答案

在您的[main.cpp]中包括了<new>，它声明了函数

In your [main.cpp] you're including <new>, which declares the function

 void* operator new( size_t size, void* p) throw()

您没有声明自己的函数.

You don't declare your own function.

因此，由new声明的函数是唯一已知的函数，并且也是被调用的函数.

Hence the function declared by new is the only one that's known, and the one that's called.

顺便说一句，请注意，C ++ 98§18.4.1.3/1禁止替换上面显示的功能(以及其他三个，即具有void*位置的new和delete的单个对象和数组形式)论点).

By the way, note that C++98 §18.4.1.3/1 prohibits replacement of the function shown above (plus three others, namely single object and array forms of new and delete with void* placement argument).

此外，尽管我在顺便说一句"中发表评论，但很可能无论新的安置方式是什么解决方案，都有可能提供更安全，更有效，更清晰的更高级别的解决方案.

Also, while I'm on the "by the way" commenting, chances are that whatever placement new is thought to be the solution of, there is probably a safer and just as efficient and more clear higher level solution.

干杯hth.，

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