5,6)若非const_cast<T*>((U*)nullptr)良构则行为未定义。 7,8)若非reinterpret_cast<T*>((U*)nullptr)良构则行为未定义。 调用右值重载(2,4,6,8)后,r为空且r.get()==nullptr,但对于dynamic_pointer_cast(4),若dynamic_cast失败则不修改r。
_cast<A*>(this), this){}};structBase{virtual~Base(){}};structDerived:Base{virtualvoidname(){}};intmain(){D d;// 最终派生对象A&a=d;// 向上转换,可以用 dynamic_cast,但不是必须的[[maybe_unused]]D&new_d=dynamic_cast<D&>(a);// 向下转换[[maybe_unused]]B&new_b=dynamic_cast<...
int n = 1; int* p1 = &n; void* pv = p1; int* p2 = static_cast<int*>(pv); std::cout << *p2 << '\n'; // prints 1If the original pointer is pointing to a base class subobject within an object of some polymorphic type, dynamic_cast may be used to obtain a void* that...
dynamic_cast and polymorphic typeid in constant expressions P1327R1 10 9 19.29 (16.10)* 11.0.3* 5.1 2021.1 20.7 12.0 11.0 Changing the active member of a union inside constexpr [FTM]* P1330R0 9 9 19.10* 11.0.3* 5.1 2021.1 20.7 12.0 11.0 Coroutines [FTM]* P0912R5 10 8 (partial...
(type)C-style cast *aIndirection(dereference) &aAddress-of sizeofSize-of[note 1] co_awaitawait-expression(C++20) newnew[]Dynamic memory allocation deletedelete[]Dynamic memory deallocation 4.*->*Pointer-to-memberLeft-to-right → 5a*ba/ba%bMultiplication, division, and remainder ...
2) 纯右值表达式不能是多态的[polymorphic]:纯右值表达式标识对象的动态型别总是表达式的型别。[the dynamic type of the object it identifies is always the type of the expression. ] 3) 非类[non-class]的纯右值不能被const或volatile关键字标识[cv-qualified]。
pointer = new type; pointer = new type( initializer ); pointer = new type[size]; new可以给数据类型分配一个新结点并返回一个指向新分配内存区的首地址. 也可以对它进行初始化.中括号中的size可以分配尺寸大小. delete 语法: return-type class-name::operator#(parameter-list) { ...
if (z == nullptr){ cout << "Z null"; } cout << *q; shared_ptr<B> r; r = dynamic_pointer_cast<B>(t); // Converts t to a shared_ptr<B> math.h, cmath (floating point math) #include <cmath> // Include cmath (std namespace) sin(x); cos(x); tan(x); // Trig...
std::bad_cast This can be thrown by dynamic_cast. std::bad_exception This is useful device to handle unexpected exceptions in a C++ program. std::bad_typeid This can be thrown by typeid. std::logic_error An exception that theoretically can be detected by reading the code. std::domain_...
the this pointer; (this指针也是纯右值,因为this也是一个地址) a lambda expression, such as [](int x){ return x * x; }.(since C++11) (lambda表达式是纯右值) Properties: Same as rvalue (below). A prvalue cannot be polymorphic: the dynamic type of the object it identifies is always the...