C ++ class member access operator -> reload
C ++ function overloading and operator overloading
Class member access operator (->) can be overloaded, but it is cumbersome. It is defined for a given class "pointer" behavior. Operator -> must be a member function. If you use the -> operator, the return type must be a pointer or a class of objects.
Operator -> is usually a pointer dereference operator * used in combination with, for achieving "smart pointer" function. These pointers are pointers behave like normal objects, the only difference is that when you pass a pointer to access the object, they perform other tasks. For example, when the pointer is destroyed, or when a pointer to another object, the object will be automatically deleted.
Indirect reference operator -> it can be defined as a unary postfix operator. That is, a given class:
class Ptr{ //... X * operator->(); };
Ptr class of objects can be used to access a member of class X,use the pointer usage is very similar. E.g:
void f(Ptr p ) { p->m = 10 ; // (p.operator->())->m = 10 }
Statement p-> m is interpreted as (p.operator -> ()) -> m. Similarly, the following example shows how to reload a class member access operator ->.
#include <iostream> #include <vector> using namespace std; // 假设一个实际的类 class Obj { static int i, j; public: void f() const { cout << i++ << endl; } void g() const { cout << j++ << endl; } }; // 静态成员定义 int Obj::i = 10; int Obj::j = 12; // 为上面的类实现一个容器 class ObjContainer { vector<Obj*> a; public: void add(Obj* obj) { a.push_back(obj); // 调用向量的标准方法 } friend class SmartPointer; }; // 实现智能指针,用于访问类 Obj 的成员 class SmartPointer { ObjContainer oc; int index; public: SmartPointer(ObjContainer& objc) { oc = objc; index = 0; } // 返回值表示列表结束 bool operator++() // 前缀版本 { if(index >= oc.a.size()) return false; if(oc.a[++index] == 0) return false; return true; } bool operator++(int) // 后缀版本 { return operator++(); } // 重载运算符 -> Obj* operator->() const { if(!oc.a[index]) { cout << "Zero value"; return (Obj*)0; } return oc.a[index]; } }; int main() { const int sz = 10; Obj o[sz]; ObjContainer oc; for(int i = 0; i < sz; i++) { oc.add(&o[i]); } SmartPointer sp(oc); // 创建一个迭代器 do { sp->f(); // 智能指针调用 sp->g(); } while(sp++); return 0; }
When the above code is compiled and executed, it produces the following results:
10 12 11 13 12 14 13 15 14 16 15 17 16 18 17 19 18 20 19 21