即使使用智能指针，C++ 也会在异常情况下泄漏

Question

我是智能指针世界的新手。我读完了，他们都说智能指针将避免内存泄漏，即使程序在遇到异常后退出也是如此。

我写了一个简单的程序来尝试这个，但是 Valgrind告诉我我的程序正在泄漏内存(三个分配，只有一个空闲)。

这是源代码:

#include <iostream>
#include <memory>

using namespace std;

int main()
{
    auto_ptr<int> ptr_int(new int(5));

    throw std::bad_alloc();

    cout << *ptr_int;
}

还有这个 Valgrind 报告:

==27862== Memcheck, a memory error detector
==27862== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==27862== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==27862== Command: ./smart_pointers
==27862== Parent PID: 5388
==27862==
==27862==
==27862== HEAP SUMMARY:
==27862==     in use at exit: 104 bytes in 2 blocks
==27862==   total heap usage: 3 allocs, 1 frees, 120 bytes allocated
==27862==
==27862== 4 bytes in 1 blocks are still reachable in loss record 1 of 2
==27862==    at 0x4026351: operator new(unsigned int) (vg_replace_malloc.c:255)
==27862==    by 0x804878A: main (smart_pointers.cpp:8)
==27862==
==27862== 100 bytes in 1 blocks are possibly lost in loss record 2 of 2
==27862==    at 0x4025BD3: malloc (vg_replace_malloc.c:236)
==27862==    by 0x40E861A: __cxa_allocate_exception (in /usr/lib/libstdc++.so.6.0.14)
==27862==    by 0x80487AE: main (smart_pointers.cpp:10)
==27862==
==27862== LEAK SUMMARY:
==27862==    definitely lost: 0 bytes in 0 blocks
==27862==    indirectly lost: 0 bytes in 0 blocks
==27862==      possibly lost: 100 bytes in 1 blocks
==27862==    still reachable: 4 bytes in 1 blocks
==27862==         suppressed: 0 bytes in 0 blocks
==27862==
==27862== For counts of detected and suppressed errors, rerun with: -v
==27862== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 19 from 8)

使用智能指针是否保证即使出现异常也会销毁分配的资源？

Answer 1

如果未处理异常，则在调用 std::terminate 之前是否展开堆栈由实现定义。

如果您处理异常，那么智能指针将按预期工作。

引用:

C++11 15.5.1 std::terminate() 函数

1 In some situations exception handling must be abandoned for less subtle error handling techniques. These situations are:

........

— when the exception handling mechanism cannot find a handler for a thrown exception , or

........

2 In such cases std::terminate() is called. In the situation where no matching handler is found, it is implementation-defined whether or not the stack is unwound before std::terminate() is called.