shared_ptr基於設計問題

Question

我在我的應用程序設計中使用shared_ptr，並且我有越來越多的對象變成堆分配而不是堆棧上的簡單對象（或更復雜對象的聚集）的趨勢。
而不是簡單的（但有可能Foo :: bar會在更復雜的情況下變成懸掛參考）...

 
struct Bar { }; 
struct Foo { Foo(Bar& bar) : bar(bar) { }; Bar& bar; }; 
int main() { 
    Bar bar; 
    Foo foo(bar); 
    // ... 
} 

... I need to do ...

 
struct Bar { }; 
struct Foo { Foo(shared_ptr bar) : bar(bar) { }; shared_ptr<Bar> bar; }; 
int main() { 
    shared_ptr<Bar> bar = make_shared<Bar>(); 
    Foo foo(bar); 
    // ... 
} 

... because I want to avoid of manual objects life-time tracking
Did I missed point in shared_ptr usage or this is pay for automatic life-time management ? Or maybe this is bad design sign ?

Answer 1

It is a question of your object life cycle. You should use shared_ptr when you really share an object between multiple other objects.

In your case the owner of FOO and BAR must control the lifecycle of both. Maybe it is possible to make BAR a private member of you class FOO and let FOO control the life cycle.

I personally use the smart pointers to express the ownership of an object. Shared_ptr means that it is really shared and I am not the only owner of this object. Scoped or unique pointer show that I am the only owner of the object. If you want to transfer the ownership you can use auto_ptr or the C++0x move semantics.

I have seen at least in bigger projects that the lack of life cycle control will lead to dangling objects. So you don't have a direct memory leak any longer because of automatic life-time management but you get circular dependencies. Which lead to the same result.

To answer your question if this is bad design. It depends on what you are doing.

Answer 2

Have you tried working on values instead of pointers ?

Answer 3

It is a sign of bad design. shared_ptr存在於您的對象必須分配堆時。您不應該因爲可以使用shared_ptr而額外分配堆中的任何內容。堆棧仍然是英里的最佳選擇。

在開始決定如何實現它之前，您需要知道哪些對象需要在堆上運行，哪些需要在堆上運行，以及擁有權是什麼。然後你可以使用shared_ptr作爲實現工具。