宏替换C ++运算符new [英] Macro to replace C++ operator new

问题描述

是否可以创建宏来替换所有形式的运算符new ，其中包含额外的args ...例如 __ FILE __ 和 __ LINE __ ？

麻烦似乎是 code>可以使用或不使用括号进行编码，因此：

• >宏：

    #define new new（__ FILE__，__LINE__）
    

  将替换以下声明：

    A * a = new A （）; 
    




• 和类似功能的宏：

    #define new（A）new（A，__FILE__，__LINE__）
     
   
   
  将替换以下声明：
    A * a = new Nothrow）A（）; 
    
   

不幸的是，具有相同的标识符的宏，即使它们具有不同的类型，因此下列操作失败：

  #define new new（__ FILE__，__LINE__）
 #define new（A）new（A，__FILE__，__LINE__）//错误：已定义new
  

因为我使用g ++我希望使用他们的语法 variadic宏会产生成功，但不幸的是，。以下：

  #define new（...）new（__ FILE__，__LINE__，## __VA_ARGS__）
  

只匹配 new（xyx）A（），而不是 new A（）。

我知道已经写了为什么这是不可能的，但我觉得我这么近必须有办法。

解决方案

这里是我使用的：

在new.cpp

  const char * __file__ =unknown 
 size_t __line__ = 0; 
 
 void * operator new（size_t size）{
 void * ptr = malloc（size）; 
 record_alloc（ptr，__ file __，__ line__）; 
 __file__ =unknown; 
 __line__ = 0; 
 return ptr; 
} 
 
 void delete（void * ptr）
 {
 unrecord_alloc（ptr）; 
 free（ptr）; 
} 
  

对于紧凑性，我省略new和delete的其他定义。 record_alloc和unrecord_alloc是保存包含ptr，line和file的结构链表的函数。

$ new $ h $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $
$ b

  extern const char * __file__; 
 extern size_t __line__; 
 #define new（__file __ = __ FILE __，__ line __ = __ LINE__）&& 0？ NULL：new 
  

对于g ++，new只扩展一次。关键是&& 0，这使它为假，并导致使用真正的新。例如，

  char * str = new char [100]; 
 

由预处理器扩展为

  char * str =（__file __ =somefile.c，__ line __ = some_number）&& 0？ NULL：new char [100]; 
  

因此，记录文件和行号，并调用您的自定义新函数。

这适用于任何形式的new - 只要在new.cpp中有一个相应的形式

Is it possible to create macros to replace all forms of operator new with overloads that include additional args...say __FILE__ and __LINE__?

The trouble appears to be that operator new can either be coded with or without parentheses, therefore:

• object-like macros:

  #define new new(__FILE__, __LINE__)
  

  will replace declarations like:

  A* a = new A();
  

• and function-like macros:

  #define new(A) new (A, __FILE__, __LINE__)
  

  will replace declarations like:

  A* a = new(std::nothrow) A();
  

Unfortunately it's an error to attempt to declare two macros with the same identifier, even if they are of different types, so the following fails:

#define new new(__FILE__, __LINE__)
#define new(A) new (A, __FILE__, __LINE__) // Error: "new" already defined

Since I'm using g++ I was hopeful that employing their syntax of variadic macros would yield success, but unfortunately not. The following:

#define new(...) new(__FILE__, __LINE__, ## __VA_ARGS__)

only matches new(xyx) A(), not new A().

I know that essays have been written about why it is impossible, but I feel like I'm so close that there must be a way. Is there anything obvious that I'm missing?

解决方案

Here is what I use:

In new.cpp

const char* __file__ = "unknown";
size_t __line__ = 0;

void* operator new(size_t size) {
    void *ptr = malloc(size);
    record_alloc(ptr,__file__,__line__);
    __file__ = "unknown";
    __line__ = 0;
    return ptr;
}

void delete(void *ptr)
{
   unrecord_alloc(ptr);
   free(ptr);
}

For compactness, I'm leaving out the other definitions of new and delete. "record_alloc" and "unrecord_alloc" are functions that maintain a linked list of structure containing ptr, line, and file).

in new.hpp

extern const char* __file__;
extern size_t __line__;
#define new (__file__=__FILE__,__line__=__LINE__) && 0 ? NULL : new

For g++, "new" is expanded only once. The key is the "&& 0" which makes it false and causes the real new to be used. For example,

char *str = new char[100];

is expanded by the preprocessor to

char *str = (__file__="somefile.c",__line__=some_number) && 0 ? NULL : new char [100];

Thus file and line number are recorded and your custom new function is called.

This works for any form of new -- as long as there is a corresponding form in new.cpp

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