1. Initialization和Assignment不一樣。其中Initialization包括direct-initialization (如A a(...))和copy-initialization (如 A a = b;)

? ? 注意A a = b為copy-initialization，

? ? 而A a; A b; a = b;為Assignment。

2. We cannot copy objects of the IO types, so we cannot use copy-initialization on objects of these types.

3. As the copy constructor is used (implicitly) to pass and return objects to and from objects, it usually should not be made explicit.

4. 為了防止復制，我們可以把拷貝構造函數設置為private，同時只在類中聲明，但不在任何地方定義。

5. Rule of Three, if you need a destructor, then you need all three copy-control members.

6. Even if we write our own destructor, the synthesized destructor is still run.

7. 編譯器會為我們生成一個拷貝構造函數，但是一旦我們自己來寫拷貝構造函數，那么我們必須對每個成員變量顯示賦值，否則成員變量由其自身的默認構造函數來賦值。

8. 簡單的Smart pointer示例。

#include <iostream>
using std::ostream; using std::cout; using std::endl;
#include <string>
#include <cstddef>
using std::size_t;
/* smart pointer class: takes ownership of the dynamically allocated*                      object to which it is bound * User code must dynamically allocate an object to initialize a HasPtr* and must not delete that object; the HasPtr class will delete it
*/
//private class for use by HasPtr only
class U_Ptr {friend class HasPtr;int *ip;size_t use;U_Ptr(int *p): ip(p), use(1) { }~U_Ptr() { cout << "U_Ptr destructor" << endl; delete ip; }
};class HasPtr {
public:// HasPtr owns the pointer; p must have been dynamically allocatedHasPtr(int *p, int i): ptr(new U_Ptr(p)), val(i) { }// copy members and increment the use countHasPtr(const HasPtr &orig):ptr(orig.ptr), val(orig.val) { ++ptr->use; }HasPtr& operator=(const HasPtr&);// if use count goes to zero, delete the U_Ptr object~HasPtr() { if (--ptr->use == 0) {cout << "HasPtr destructor" << endl;delete ptr; }} friend ostream& operator<<(ostream&, const HasPtr&);// copy control and constructors as before// accessors must change to fetch value from U_Ptr objectint *get_ptr() const { return ptr->ip; } int get_int() const { return val; }// change the appropriate data membervoid set_ptr(int *p) { ptr->ip = p; }void set_int(int i) { val = i; }// return or change the value pointed to, so ok for const objects// Note: *ptr->ip is equivalent to *(ptr->ip)int get_ptr_val() const { return *ptr->ip; } void set_ptr_val(int i) { *ptr->ip = i; }
private:U_Ptr *ptr;        // points to use-counted U_Ptr classint val;
};HasPtr& HasPtr::operator=(const HasPtr &rhs)
{++rhs.ptr->use;     // increment use count on rhs firstif (--ptr->use == 0) {cout << "operator= delete" << endl;delete ptr;    // if use count goes to 0 on this object, delete it
    }ptr = rhs.ptr;      // copy the U_Ptr objectval = rhs.val;      // copy the int memberreturn *this;
}ostream& operator<<(ostream &os, const HasPtr &hp)
{os << "*ptr: " << hp.get_ptr_val() << "\tval: " << hp.get_int() << endl;return os;
}int main()
{int *obj = new int(0);HasPtr ptr1(obj, 42);HasPtr ptr2(ptr1);cout << "(1) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl;ptr1.set_ptr_val(42); // sets object to which both ptr1 and ptr2 pointptr2.get_ptr_val();   // returns 42
cout << "(2) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl;ptr1.set_int(0);   // changes s member only in ptr1ptr2.get_int();    // returns 42ptr1.get_int();    // returns 0
cout << "(3) ptr1: " << ptr1 << endl << "ptr2: " << ptr2 << endl;
}

9. Define Valuelike Class

? ??構造函數和析構函數

轉載于:https://www.cnblogs.com/null00/archive/2013/05/31/3107928.html

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