Visual Studio C++ 项目中的奇怪内存泄漏

Question

我用unique_ptr。为了创建这个指针，我使用了这个代码片段：

template<typename T, typename ...Args>
std::unique_ptr<T> make_unique(Args&& ...args)
{
    return std::unique_ptr<T>(new T(std::forward<Args>(args)...)); //line 44
}

我在帮助 built-in memory leak checker 的帮助下测试我的项目是否存在内存泄漏。

我得到以下结果：

Detected memory leaks!
Dumping objects ->
my_header.h(44) : {228} normal block at 0x008AD568, 8 bytes long.
 Data: <        > A0 CB 8A 00 01 00 00 00 
my_header.h(44) : {226} normal block at 0x008AD5B8, 8 bytes long.
 Data: <        > 00 D6 8A 00 00 00 00 00 
/////////////////this error repeats many times

此外，我使用 deleaker。这个工具说，没有内存泄漏。

Answer 1

您不应该使用 release() unless you're handing off the pointer-raw to someone else (hopefully another std::unique_ptr or a std::shared_ptr, etc). Instead you should be using reset()，或者只是让 scope-exit 为您销毁托管对象。

使用您的代码演示好坏的最简单示例：

不好：使用release()

#include <memory>

namespace
{
    template<typename T, typename ...Args>
    std::unique_ptr<T> make_unique(Args&& ...args)
    {
        return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
    }
}

int main()
{
    std::unique_ptr<int> ptr = make_unique<int>(5);
    ptr.release();
}

Valgrind 输出

==29012== 4 bytes in 1 blocks are definitely lost in loss record 1 of 87
==29012==    at 0x10003B51B: malloc (vg_replace_malloc.c:303)
==29012==    by 0x1001CD43D: operator new(unsigned long) (in /usr/lib/libc++.1.dylib)
==29012==    by 0x10000147B: std::__1::unique_ptr<int, std::__1::default_delete<int> > (anonymous namespace)::make_unique<int, int>(int&&) (in ./Sample C++)
==29012==    by 0x100001337: main (in ./Sample C++)
==29012== 
==29012== LEAK SUMMARY:
==29012==    definitely lost: 4 bytes in 1 blocks
==29012==    indirectly lost: 0 bytes in 0 blocks
==29012==      possibly lost: 0 bytes in 0 blocks
==29012==    still reachable: 192 bytes in 6 blocks
==29012==         suppressed: 35,164 bytes in 435 blocks
==29012== Reachable blocks (those to which a pointer was found) are not shown.
==29012== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==29012== 
==29012== For counts of detected and suppressed errors, rerun with: -v
==29012== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 17 from 17)

好：使用reset()

#include <memory>

namespace
{
    template<typename T, typename ...Args>
    std::unique_ptr<T> make_unique(Args&& ...args)
    {
        return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
    }
}

int main()
{
    std::unique_ptr<int> ptr = make_unique<int>(5);
    ptr.reset(); // HERE
}

Valgrind 输出

==29045== HEAP SUMMARY:
==29045==     in use at exit: 35,356 bytes in 441 blocks
==29045==   total heap usage: 508 allocs, 67 frees, 41,216 bytes allocated
==29045== 
==29045== LEAK SUMMARY:
==29045==    definitely lost: 0 bytes in 0 blocks
==29045==    indirectly lost: 0 bytes in 0 blocks
==29045==      possibly lost: 0 bytes in 0 blocks
==29045==    still reachable: 192 bytes in 6 blocks
==29045==         suppressed: 35,164 bytes in 435 blocks
==29045== Reachable blocks (those to which a pointer was found) are not shown.
==29045== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==29045== 
==29045== For counts of detected and suppressed errors, rerun with: -v
==29045== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 17 from 17)

只需完全删除 main() 中的第二行即可收到与上面相同的输出（Good）。

int main()
{
    std::unique_ptr<int> ptr = make_unique<int>(5);
}

同样如此：

int main()
{
    std::unique_ptr<int> ptr = make_unique<int>(5);
    std::unique_ptr<int> other(ptr.release());
}

祝你好运。

Visual Studio C++ 项目中的奇怪内存泄漏

Weird memory leak in Visual Studio C++ project

c++

c++11

visual-studio-2013

memory-leaks