我已经看到关于此主题的其他一些问题，但仍未找到答案 - 我想我错过了一些东西：
我定义了两个简单的测试类：
I defined two simple test classes:
class TestBase { public: TestBase ( ) { }; ~ TestBase ( ) { }; protected: inline virtual int getInt ( ) { return 0; } }; class TestDerived : public TestBase { protected: inline int getInt ( ) override { return 1; } };我使用 std :: shared_ptr声明typedefs以简化它们的使用：
typedef std::shared_ptr<TestBase> spBase; typedef std::shared_ptr<TestDerived> spDerived;问题：我无法编译代码来使用这些 shared_ptr
Problem: I cannot compile code to use these shared_ptr declarations polymorphically, even though base in all these cases is actually an instance of spDerived:
spBase base; spDerived derived = static_cast < spDerived > ( base );错误：没有匹配函数调用'std :: shared_ptr :: shared_ptr（spBase&）
error: no matching function for call to ‘std::shared_ptr::shared_ptr(spBase&)
spDerived derived = dynamic_cast < spDerived > ( base );error：can not dynamic_cast'base'（type'spBase {aka class std :: shared_ptr}'（target不是指针或引用）
error: cannot dynamic_cast ‘base’ (of type ‘spBase {aka class std::shared_ptr}’) to type ‘spDerived {aka class std::shared_ptr}’ (target is not pointer or reference)
spDerived derived = static_pointer_cast < spDerived > ( base );错误：从'std :: shared_ptr'转换为非标量键入'spDerived {aka std :: shared_ptr}'请求 $ b
error: conversion from ‘std::shared_ptr >’ to non-scalar type ‘spDerived {aka std::shared_ptr}’ requested
spDerived derived = dynamic_pointer_cast < spDerived > ( base );错误：从'std :: shared_ptr'转换为非标量键入'spDerived {aka std :: shared_ptr}'请求
error: conversion from ‘std::shared_ptr >’ to non-scalar type ‘spDerived {aka std::shared_ptr}’ requested
在默认的GCC工具链的Ubuntu 14.04盒子上使用C ++ 11。编译器是gcc-4.9。 我做错了什么？不能使用多态的shared_pointer？
I'm using C++11 on an Ubuntu 14.04 box with the default GCC tool chain. Compiler is gcc-4.9. What am I doing wrong? Can't a shared_pointer be used polymorphically?
推荐答案传入 std :: static_pointer_cast 和 std :: dynamic_pointer_cast 作为第一个类型模板参数是转换的指针类型本身的类型，而不是 smart 指针类型：
static_pointer_cast<T>(arg); .~~~^ v template <class T, class U> .~~~~^ v shared_ptr<T> static_pointer_cast(const shared_ptr<U>& r); dynamic_pointer_cast<T>(arg); .~~~~^ v template <class T, class U> .~~~~^ v shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& r);有了这个说法，你可以这样称呼它：
With that said, you could call it like below:
spBase base = std::make_shared<TestDerived>(); spDerived derived = std::dynamic_pointer_cast<spDerived::element_type>(base); // or: spDerived derived2 = std::dynamic_pointer_cast<TestDerived>(base);更多推荐
我如何使用std :: shared
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