如何使用boost :: smart_ptr在多态性？ [英] How to use boost::smart_ptr in polymorphism?

问题描述

Boost智能指针可用于多态性，但如何

Boost smart pointers can be used with polymorphism, but how do you cast the subclass back to the pointer?

using namespace boost;
// ...
shared_ptr<SuperClass> a_ptr(new SubClass);
// ...
shared_ptr<SubClass> b_ptr = (shared_ptr<SubClass>)a_ptr; // Doesn't compile

最后一行不编译，并给出错误C2440：'type cast'：无法从'boost :: shared_ptr < T> '转换为'boost :: shared_ptr < T& c> c>

The last line doesn't compile and gives error C2440: 'type cast' : cannot convert from 'boost::shared_ptr<T>' to 'boost::shared_ptr<T>'

推荐答案

static_pointer_cast ：

You need to use static_pointer_cast:

struct B { virtual ~B() { } };
struct D : B { };

shared_ptr<B> bp(new D);
shared_ptr<D> dp(static_pointer_cast<D>(b));

（还有 dynamic_pointer_cast 和 const_pointer_cast 分别用于执行动态和常量转换。）

(There are also dynamic_pointer_cast and const_pointer_cast for performing dynamic and const casts respectively.)

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