#define new DEBUG_NEW

转载于 2016-08-19 23:45:15 发布 · 584 阅读

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本文详细解析了VC++中DEBUG_NEW宏的作用及其在调试内存泄漏时的应用。通过使用DEBUG_NEW，开发者能在debug模式下追踪到每个对象的分配位置，从而有效定位内存泄漏问题。

在用vc时，利用AppWizard会产生如下代码：

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

对于

#define new DEBUG_NEW
首先看msdn的解释：

Assists in finding memory leaks. You can use DEBUG_NEW everywhere in your program that you would ordinarily use the new operator to allocate heap storage.

In debug mode (when the _DEBUG symbol is defined), DEBUG_NEW keeps track of the filename and line number for each object that it allocates. Then, when you use the CMemoryState::DumpAllObjectsSince member function, each object allocated with DEBUG_NEW is shown with the filename and line number where it was allocated.

To use DEBUG_NEW, insert the following directive into your source files:

#define new DEBUG_NEW

Once you insert this directive, the preprocessor will insert DEBUG_NEW wherever you use new, and MFC does the rest. When you compile a release version of your program, DEBUG_NEW resolves to a simple newoperation, and the filename and line number information is not generated.

再查看定义：

#ifdef _DEBUG

void* AFX_CDECL operator new(size_t nSize, LPCSTR lpszFileName, int nLine);
#define DEBUG_NEW new(THIS_FILE, __LINE__)

#else

#define DEBUG_NEW new

#endif

这样就很清楚了，当在debug模式下时，我们分配内存时的new被替换成DEBUG_NEW，而这个DEBUG_NEW不仅要传入内存块的大小，还要传入源文件名和行号，这就有个好处，即当发生内存泄漏时，我们可以在调试模式下定位到该问题代码处。若删掉该句，就不能进行定位了。而在release版本下的new就是简单的new，并不会传入文件名和行号。

因此，我们在开发代码阶段，保留上述代码是值得的。