如何使用Valgrind調試C++記憶體洩漏？

如何使用Valgrind 偵錯C++ 記憶體洩漏

Valgrind 是一個功能強大的記憶體偵錯器，可用於偵測C++ 程式中的記憶體洩漏、非法使用和分配問題。以下介紹如何使用Valgrind 偵錯C++ 記憶體洩漏：

1. 安裝Valgrind

使用以下指令安裝Valgrind：

sudo apt install valgrind

2.編譯和偵錯

在編譯程式時，新增-g 標記以產生偵錯資訊：

g++ -g my_program.cpp -o my_program

然後，使用Valgrind 運行程序，並使用 --leak-check=full 標記來檢查記憶體洩漏：

valgrind --leak-check=full ./my_program

#3. 分析Valgrind 輸出

Valgrind 的輸出將包含有關偵測到的記憶體洩漏的訊息。

實戰案例

以下是模擬記憶體洩漏的簡單C++ 程式：

#include <iostream>

int* leak() {
  int* ptr = new int;
  return ptr;
}

int main() {
  int* ptr = leak();
  return 0;
}

編譯並使用Valgrind 執行此程式：

g++ -g leak.cpp -o leak
valgrind --leak-check=full ./leak

Valgrind 的輸出將包含以下資訊：

==27244== Memcheck, a memory error detector
==27244== Copyright (C) 2002-2017, and GNU GPL'd by, Julian Seward et al.
==27244== Using Valgrind-3.15.0.
==27244== Command: ./leak
==27244==
==27244== HEAP SUMMARY:
==27244==     in use at exit: 4 bytes in 1 blocks
==27244==   total heap usage: 1 allocs, 0 frees, 4 bytes allocated
==27244==
==27244== LEAK SUMMARY:
==27244==    definitely lost: 4 bytes in 1 blocks
==27244==    indirectly lost: 0 bytes in 0 blocks
==27244==      possibly lost: 0 bytes in 0 blocks
==27244==    still reachable: 0 bytes in 0 blocks
==27244==         suppressed: 0 bytes in 0 blocks
==27244== Rerun with --leak-check=full to see what's still reachable
==27244==
==27244== For counts of detected and suppressed errors, rerun with: -v
==27244== Use --track-origins=yes to see where unfreed memory was allocated
==27244== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
==27244==
==27244== 1 errors in context 0 of 1:
==27244== Invalid read of size 8
==27244==    at 0x4842E10: leak (leak.cpp:5)
==27244==    by 0x483D8E7: main (leak.cpp:12)
==27244==  Address 0x555555555600 is not stack'd, malloc'd or (recently) free'd
==27244==
==27244== LEAK SUMMARY:
==27244==    definitely lost: 0 bytes in 0 blocks
==27244==    indirectly lost: 0 bytes in 0 blocks
==27244==      possibly lost: 4 bytes in 1 blocks
==27244==    still reachable: 0 bytes in 0 blocks
==27244==         suppressed: 0 bytes in 0 blocks
==27244== Rerun with --leak-check=full to see what's still reachable
==27244==
==27244== For counts of detected and suppressed errors, rerun with: -v
==27244== Use --track-origins=yes to see where unfreed memory was allocated

此輸出表示程式中存在4 個位元組的記憶體洩漏，該洩漏來自函數leak() 中未釋放的int 指標。

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