[英]How to prevent deletion of a raw pointer that is used as shared pointer?
I implemented a C-API for a C++ class which uses shared-pointers of other objects to access them. 我为C ++类实现了C-API,该类使用其他对象的共享指针来访问它们。 In my C-API I can of course only get raw pointers.
在我的C-API中,我当然只能获得原始指针。 So I "convert" the raw pointer in my C-API to a shared-pointer and use this then with my C++ class methods:
因此,我将C-API中的原始指针“转换”为共享指针,然后将其与我的C ++类方法一起使用:
method(std::shared_ptr<dataType>(raw-pointer));
Now I have the problem that at the end of "method" always the shared-pointer destructor is called and it unfortunately kills the object my raw-pointer is pointing at (which I don't want). 现在,我遇到的问题是,在“方法”的末尾,总是会调用共享指针析构函数,并且不幸的是,它杀死了我的原始指针指向的对象(我不想要)。 So, how can I prevent the raw-pointer from being killed?
因此,如何防止原始指针被杀死?
I already tried shared-pointer functions like reset() or swap(), but they all didn't let my raw-pointer go... 我已经尝试过像reset()或swap()这样的共享指针功能,但是它们都没有让我的原始指针走...
bool Traffic_doStep(traffic_handle t, environment_handle e, double cycletime) {
if (!valid(t, __FUNCTION__)) return false;
if (!valid(e, __FUNCTION__)) return false;
if (!valid(cycletime, __FUNCTION__)) return false;
try {
t->doStep(std::shared_ptr<Environment>(e), cycletime);
return true;
}
catch (const std::exception& e) {
std::cerr << e.what() << std::endl;
return false;
}
}
Expected result would be that the raw-pointer e is still pointing to a valid object after this function returned. 预期的结果是,此函数返回后,原始指针e仍指向有效对象。 Actually the raw-pointer points then to a deleted object.
实际上,原始指针然后指向已删除的对象。
std::shared_ptr
std::shared_ptr
The purpose of Smart Pointers in C++ is to provide automatic Lifetime management. C ++中的智能指针的目的是提供自动的生命周期管理。 When you write
std::shared_ptr<int> ptr{raw_ptr};
当您编写
std::shared_ptr<int> ptr{raw_ptr};
, the expectation is that when ptr
goes out of scope, the object pointed to by raw_ptr
will be delete
'd. ,期望是当
ptr
超出范围时, raw_ptr
指向的对象将被delete
。 If this is not the intent, then you should not be placing the pointer in a smart pointer. 如果这不是目的,则不应将指针放在智能指针中。
So if your application does not manage the lifetime of a pointer, then it is perfectly acceptable to store a raw pointer. 因此,如果您的应用程序无法管理指针的生存期,那么存储原始指针是完全可以接受的。
If the API behind the function cannot be altered, you will instead need to construct the std::shared_ptr
with a no-op deleter function, so that when clean-up is called, nothing will happen to the pointer. 如果该函数后面的API无法更改,则将需要使用无操作删除器函数构造
std::shared_ptr
,以便在调用清理时指针不会发生任何变化。
try {
std::shared_ptr<Environment> temp_ptr{e, [](int *) {}/*No-Op Deleter*/};
t->doStep(temp_ptr, cycletime);
return true;
}
This will solve your problem, but this is, of course, an Antipattern; 这将解决您的问题,但这当然是反模式; don't do this unless you've been forced to by API design constraints that you cannot control.
除非您因无法控制的API设计约束而被迫这样做,否则请不要这样做。
You may provide a custom deleter of a shared pointer. 您可以提供共享指针的自定义删除器。
Here is a viable constructor: 这是一个可行的构造函数:
template< class Y, class Deleter >
shared_ptr( Y* ptr, Deleter d );
But I would rather use a unique pointer and then release it. 但是我宁愿使用唯一的指针然后释放它。
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