C++笔记

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这篇博客探讨了C++中对象的拷贝构造函数、浅拷贝与深拷贝的概念，以及`this`指针和友元函数在内存管理中的应用。通过示例代码详细解释了如何在类设计中处理对象复制和内存分配问题，以确保正确性和效率。

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#include<iostream>
#include<Cstring>
#include<cstdlib>
using namespace std;
class Student
{
private:
	char name[20];
	int age;
	int num;
public:
	Student(int n, char* str, int s);
	~Student();
	void print();
	void set(int n, char* str, int a);
};

void Student::print()
{
	cout << name << "   " << num << "   " << age << endl;
}

Student::Student(int n, char* str, int a)
{
	num = n;
	strcpy_s(name,str);
	age = a;
}

void Student::set(int n, char* str, int a)
{
	num = n;
	strcpy_s(name, str);
	age = a;
}

Student::~Student()
{
	cout << name << "   " << num << "   " << age << endl;
}


int main()
{
	char name[20] = "lheng0";
	char name1[20] = "lheng1";

	char* p = name;
	Student A(102, p, 21);
	p = name1;
	Student B(102, p, 21);

	//A.set(1002, "liwensheng", 21);
	//A.print();

	return 0;
}

拷贝构造函数

#include<iostream>
using namespace std;
#define PI 3.1415926

class Circle
{
public:
	Circle(double R);
	Circle(Circle &A);
	double area();
	double girth();
private:
	double R;
};

Circle::Circle(double R)
{
	cout << "Constructor" << endl;
	this->R = R;
}

Circle::Circle(Circle& A)
{
	cout << "copy Constructor" << endl;
	this->R = A.R;
}

double Circle::area()
{
	return PI * R * R;
}

double Circle::girth()在这里插入代码片
{
	return PI * 2 * R;
}

int main()
{
	//第一次定义的A对象调用带参数的构造函数
	Circle A(5);
	//第二个B对象由于是通过A对象来初始化
	Circle B(A);
	return 0;

浅拷贝

#include<iostream>
using namespace std;
#define PI 3.1415926

class Circle
{
public:
	Circle(double R,char*str);
	//Circle(Circle &A);
	~Circle();
	double area();
	double girth();
private:
	double R;
	char* str;
};

Circle::Circle(double R, char* str)
{
	cout << "Constructor" << endl;
	this->R = R;
	this->str = new char[strlen(str)+1];
	strcpy(this->str, str);
	cout << this->R << " " << this->str << endl;
}

//Circle::Circle(Circle& A)
//{
//	delete[]str;
//}

Circle::~Circle()
{
	delete[]str;
}

double Circle::area()
{
	return PI * R * R;
}

double Circle::girth()
{
	return PI * 2 * R;
}

int main()
{
	char name[20]= "NO1.Old class";
	//第一次定义的A对象调用带参数的构造函数
	Circle A(5, name);
	//第二个B对象由于是通过A对象来初始化
	Circle B(A);
	return 0;
}

深拷贝


#include<iostream>
using namespace std;
#define PI 3.1415926

class Circle
{
public:
	Circle(double R, char* str);
	Circle(Circle &A);
	~Circle();
	double area();
	double girth();
private:
	double R;
	char* str;
};

Circle::Circle(double R, char* str)
{
	cout << "Constructor" << endl;
	this->R = R;
	this->str = new char[strlen(str) + 1];
	strcpy(this->str, str);
	cout << this->R << " " << this->str << endl;
}

Circle::Circle(Circle& A)
{
	cout << "Copy Constructor" << endl;
	this->R = A.R;
	this->str = new char[strlen(A.str) + 1];
	strcpy(this->str, A.str);
}

Circle::~Circle()
{
	delete[]str;
}

double Circle::area()
{
	return PI * R * R;
}

double Circle::girth()
{
	return PI * 2 * R;
}

int main()
{
	char name[20] = "NO1.Old class";
	//第一次定义的A对象调用带参数的构造函数
	Circle A(5, name);
	//第二个B对象由于是通过A对象来初始化
	Circle B(A);
	return 0;
}

this指针

#include<iostream>
using namespace std;
class Clock
{
public:
	int SetTime(int h, int m, int s);
	void print();
private:
	int H;
	int M;
	int S;
};
int Clock::SetTime(int h, int m, int s)
{
	/*this->H = h;
	this->M = m;
	this->S = s;*/
	(*this).H = h;
	(*this).M = m;
	(*this).S = s;
	return 0;
}
void Clock::print()
{
	cout << this->H << ":" << this->M<< ":"<< this->S;
}
int main()
{
	Clock C;
	C.SetTime(23,59,0); 
	C.print();
	return 0;
}

友元函数friend
求两点距离

#include<iostream>
using namespace std;
class Point
{
private:
	double x;
	double y;
public:
	Point(double a, double b);//构造函数
	friend double Distance(Point &a, Point &b);
};
//构造函数
Point::Point(double a, double b)
{
	this->x = a;
	this->y = b;
}
double Distance(Point& a, Point& b)
{
	double xx = a.x - b.x;
	double yy = a.y - b.y;
	return sqrt(xx* xx+yy*yy);
}
int main()
{	
	Point a(2.0,3.0);
	Point b(1.0,2.0);
	double dis = Distance(a,b);
	cout << dis << endl;
	return 0;
}

友元类
求原点到点的距离

#include<iostream>
using namespace std;
class Point
{
private:
	double x;
	double y;
public:
	Point(double a, double b);//构造函数
	friend class Tool;
};
//构造函数
Point::Point(double a, double b)
{
	this->x = a;
	this->y = b;
}
class Tool
{
public:
	double Distance(Point& b)
	{
		return sqrt(b.x * b.x + b.y * b.y);
	}
};
//点到原点距离
int main()
{	
	Point a(2.0,3.0);
	Tool t;
	double dis=t.Distance(a);
	cout << dis << endl;
	return 0;
}