为什么 valgrind 没有检测到由于 realloc 而导致的这种可能的内存泄漏？

Question

我不明白为什么 valgrind（3.14 版）在这个程序中没有检测到可能的内存泄漏：

#include <stdlib.h>

int main() {
  int *p = malloc(sizeof(int));
  p = realloc(p, 2 * sizeof(int));

  free(p);

  return 0;
}

C99 标准（ISO/IEC 9899:1999，第 314 页）对 realloc 说：

If memory for the new object cannot be allocated, the old object is not deallocated and its value is unchanged. [...] The realloc function returns a pointer to the new object (which may have the same value as a pointer to the old object), or a null pointer if the new object could not be allocated.

所以可能会出现p是NULL但是之前用malloc分配的内存单元还在，这应该不会是内存泄漏吧？

如果我用 gcc -std=c99 编译程序并用 --tool=memcheck --leak-check=full --track-origins=yes 执行 valgrind，它会给出以下消息：

==313618== Memcheck, a memory error detector
==313618== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==313618== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==313618== Command: ./a.out
==313618== 
==313618== 
==313618== HEAP SUMMARY:
==313618==     in use at exit: 0 bytes in 0 blocks
==313618==   total heap usage: 2 allocs, 2 frees, 12 bytes allocated
==313618== 
==313618== All heap blocks were freed -- no leaks are possible
==313618== 
==313618== For counts of detected and suppressed errors, rerun with: -v
==313618== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Answer 1

Valgrind 不会分析您的代码；它会分析您的代码所采取的操作。

在这个特定的运行 realloc 中没有失败，所以没有内存泄漏，所以 valgrind 没有什么可报告的：

All heap blocks were freed

这就是 valgrind 所知道的。

要检测代码中的问题，您需要静态代码分析工具。

为什么 valgrind 没有检测到由于 realloc 而导致的这种可能的内存泄漏？

Why doesn't valgrind detect this possible memory leak due to realloc?

c

valgrind

memory-leaks

realloc

dynamic-memory-allocation