Valgrind 绝对丢失并且可以通过 exit 与 main return

Question

如果我以 return 0; 退出 main，Valgrind 报告肯定丢失了内存，但如果我以 exit(0);.

退出 main，则报告仍然可以访问内存

测试-reachable.c:

#include <stdlib.h>

int main() {
  void *data = malloc(256);
  exit(0);
}

测试-lost.c:

#include <stdlib.h>

int main() {
  void *data = malloc(256);
  return 0;
}

行为：

$ gcc test-reachable.c -o test-reachable
$ valgrind --leak-check=yes ./test-reachable
==7696== Memcheck, a memory error detector
==7696== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==7696== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==7696== Command: ./test-reachable
==7696== 
==7696== 
==7696== HEAP SUMMARY:
==7696==     in use at exit: 256 bytes in 1 blocks
==7696==   total heap usage: 1 allocs, 0 frees, 256 bytes allocated
==7696== 
==7696== LEAK SUMMARY:
==7696==    definitely lost: 0 bytes in 0 blocks
==7696==    indirectly lost: 0 bytes in 0 blocks
==7696==      possibly lost: 0 bytes in 0 blocks
==7696==    still reachable: 256 bytes in 1 blocks
==7696==         suppressed: 0 bytes in 0 blocks
==7696== Reachable blocks (those to which a pointer was found) are not shown.
==7696== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==7696== 
==7696== For counts of detected and suppressed errors, rerun with: -v
==7696== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$ gcc test-lost.c -o test-lost
$ valgrind --leak-check=yes ./test-lost
==7774== Memcheck, a memory error detector
==7774== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==7774== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==7774== Command: ./test-lost
==7774== 
==7774== 
==7774== HEAP SUMMARY:
==7774==     in use at exit: 256 bytes in 1 blocks
==7774==   total heap usage: 1 allocs, 0 frees, 256 bytes allocated
==7774== 
==7774== 256 bytes in 1 blocks are definitely lost in loss record 1 of 1
==7774==    at 0x4C2C080: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7774==    by 0x40051C: main (in /tmp/test-lost)
==7774== 
==7774== LEAK SUMMARY:
==7774==    definitely lost: 256 bytes in 1 blocks
==7774==    indirectly lost: 0 bytes in 0 blocks
==7774==      possibly lost: 0 bytes in 0 blocks
==7774==    still reachable: 0 bytes in 0 blocks
==7774==         suppressed: 0 bytes in 0 blocks
==7774== 
==7774== For counts of detected and suppressed errors, rerun with: -v
==7774== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

这些行为不应该一样吗？

Answer 1

在 C++ 中，当调用 main() 中的 return 时，将为局部作用域的对象调用析构函数，而如果调用 exit()，则不会为局部作用域的对象调用析构函数. 我认为这在 C 中与在堆栈上分配的对象类似。

这可能解释了为什么在 return 的情况下，未释放的内存被视为肯定丢失，而在 exit(0) 的情况下，内存被报告为仍然可以访问。

Answer 2

Shouldn't these behave the same?

没有

在test-reachable.c中，程序退出时内存被栈变量data引用，所以仍然可以访问，而在test-[=18=中] 内存不再被引用，因为main函数已经返回，引用不存在了，内存肯定丢失了。

Valgrind 绝对丢失并且可以通过 exit 与 main return

Valgrind definitely lost and reachable with exit vs main return

c

valgrind