Copy construction and copy assignment of C + +

Copy construction and copy assignment------a somewhat difficult question.

Before we introduce, we need to first understand the difference between deep copy and shallow copy: What is deep copy, deep copy does not copy pointer, but the target object has a separate resource, the resource is copied from the meta-object, that is, to find the object's pointer, to copy its contents through the pointer;

What is a shallow copy, that is, the address of the assignment pointer, does not assign a pointer to the target, it is easy to throw a double free exception, that is, multiple targets pointing to the same memory;

Default copy constructor and default copy assignment function

If a class does not show the definition of a copy constructor and a copy assignment operator, the compiler provides one for it by default, but the function can only be shallow copies;

If a class has a member variable for a pointer and maintains a dynamically allocated memory resource with a pointer, define the copy constructor and copy assignment operator functions that support the deep copy for the class.

What's the next question?

Copy construction: T::t (T const& that) {} allocating resources, copying content

Copy Assignment:t& operator= (T const& r) {} Prevents self-assignment, allocates new resources, frees old resources, duplicates new content, and returns self-references;

To prevent misuse, we can also privatize the two to prevent misuse;

Below is a section of code for reference:

#include <iostream>

using namespace Std;

Class integer{

Public

Integer (int num): I (new int (num)) {}

Integer (integer& const that): I (new int (*that.i)) {}

integer& operatot= (Integer const& R) {

*I=*R.I;

return *i;

}

~integer () {

Delete I;

}

void const& GetValue () const{

cout<<*i<<endl;

}

Private

int* i;

Integer (const integer& that);

integer& operator (Integer const& R);

};

int main () {

Integer I1 (Ten), i2=i1;

I1.getvalue ();

I2.getvalue ();

return 0;

}

Copy construction and copy assignment of C + +