在这个例子中,Base类的析构函数是虚函数,Derived类覆盖了Base类的虚函数foo。我们通过std::unique_ptr管理一个Derived对象,并通过基类指针调用派生类的虚函数。 4.3.2 智能指针的类型转换 智能指针也支持动态类型转换,如std::dynamic_pointer_cast,它可以将基类的智能指针转换为派生类的智能指针。这在处理复杂的类层...
c)Otherwise, the runtime check fails. If the dynamic_cast is used on pointers, the null pointer value of typenew_typeis returned. If it was used on references, the exceptionstd::bad_castis thrown. 6)Whendynamic_castis used in a constructor or a destructor (directly or indirectly), ande...
输出结果是:Null pointer on second type-cast 两个dynamic_cast都是下行转换,第一个转换是安全的,因为指向对象的本质是子类,转换的结果使子类指针指向子类,天经地义;第二个转换是不安全的,因为指向对象的本质是父类,“指鹿为马”或指向不存在的空间很可能发生! 最后补充一个特殊情况,当待转换指针是void*或者转...
#include<iostream>#include<memory>using namespace std;voidCheck(weak_ptr<int>&wp){shared_ptr<int>sp=wp.lock();//获得shared_ptr<int>实例if(sp!=nullptr)cout<<"still "<<*sp<<endl;elsecout<<"pointer is invalid."<<endl;}intmain(){shared_ptr<int>sp1(newint(40));shared_ptr<int>sp2=...
C++引入了static_cast、dynamic_cast、const_cast和reinterpret_cast这4种类型转换操作符，提供了更安全、...
在类层次上进行转换的时候 dynamic_cast于static_cast的效果一样! 他返回一个新类型的值,或者会抛出一个异常! 来看代码: #include<iostream> using namespace std; struct V { virtual void f() {}; // must be polymorphic to use runtime-checked dynamic_cast ...
C++中是允许裸指针,因此裸指针之间转换方法同C语言指针强转,智能指针转换不能通过上述方法进行强转,必须通过库提供转换函数进行转换。 C++11的方法是:std::dynamic_pointer_cast;boost中的方法是:boost::dynamic_pointer_cast #include #include #include
base class type, a glvalue of an unambiguous non-virtual base class type, or a pointer to ...
. You can use it for more than just casting downwards -- you can cast sideways or even up another chain. Thedynamic_castwill seek out the desired object and return it if possible. If it can't, it will returnnullptrin the case of a pointer, or throwstd::bad_castin the case of a...
C-style cast or function-style cast) int main() { const char* s1 = u8"test"; // C2440 under /std:c++20 or /Zc:char8_t, OK in C++17 const char8_t* s2 = u8"test"; // OK under /std:c++20 or /Zc:char8_t, C4430 in C++17 const char* s3 = reinterpret_cast<const char...