以下代碼常常在一個(gè)類文件的開頭出現(xiàn)，是什么意思呢？

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

先看MSDN里的解釋：

Remarks

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 new operation, and the filename and line number information is not generated.

?

? ? 這樣就很清楚了，當(dāng)在debug模式下時(shí)，我們分配內(nèi)存時(shí)的new被替換成DEBUG_NEW，而這個(gè)DEBUG_NEW不僅要傳入內(nèi)存塊的大小，還要傳入源文件名和行號(hào)，這就有個(gè)好處，即當(dāng)發(fā)生內(nèi)存泄漏時(shí)，我們可以在調(diào)試模式下定位到該問(wèn)題代碼處。若刪掉該句，就不能進(jìn)行定位了。而在release版本下的new就是簡(jiǎn)單的new，并不會(huì)傳入文件名和行號(hào)。
? ? 如果定義了_DEBUG，表示在調(diào)試狀態(tài)下編譯，因此相應(yīng)修改了兩個(gè)符號(hào)的定義THIS_FILE是一個(gè)char數(shù)組全局變量，字符串值為當(dāng)前文件的全路徑，這樣在Debug版本中當(dāng)程序出錯(cuò)時(shí)出錯(cuò)處理代碼可用這個(gè)變量告訴你是哪個(gè)文件中的代碼有問(wèn)題。

轉(zhuǎn)載于:https://www.cnblogs.com/imapla/archive/2012/09/03/2668859.html

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