C++复制构造函数以及赋值运算符重载

//statement.h
#ifndef STATEMENT_H_
#define STATEMENT_H_
#include<iostream>
using std::cout;
using std::cin;
using std::ostream;
using std::istream;
class String
{
private:
	char *str;
	int len;
	static int num;
public:
	String();
	String(const String &);//构造深度复制构造函数
	String(const char *s);
	~String();//对于用new创建的的构造函数来说，需要析构函数执行delete操作
	int get_len(){ return len; }
	static int get_num();//静态成员函数为整个类对象共享，只能调用静态数据成员
	String& operator=(const char *s);
	String& operator=(const String&);
	char& operator[](const int i);
	const char& operator[](const int i) const;//对于const对象
	friend bool operator>(const String &str1, const String &str2);
	friend bool operator<(const String &str1, const String &str2);
	friend bool operator==(const String &str1, const String &str2);
	friend String operator+(const String &str1,const String &str2);
	friend ostream & operator<<(ostream &os, const String &str1);
	friend istream& operator>>(istream &is, String &str1);
};
#endif //STATEMENT_H_

//define.cpp
/**
*Copyright U+00A9 2018 XXXXXXX. All Right Reserved.
*Filename:
*Author:XXXXXX
*Date:2018.12.01
*Version:VS 2013
*Description:
**/

#include<iostream>
#include<cstring>
//#include<cstdlib>
#include"statement.h"
#define MAXSIZE 100
using namespace std;
int String::num = 0;//单独赋值不属于任何一个对象
int String::get_num()
{
	return num;
}
String::String()
{
	len = 1;
	str = new char[1];
	str[0] = '\0';//为了配合delete[] str  /*nullptr空指针*/
	++num;
}
String::String(const String &s)
{
	len = s.len;
	str = new char[len + 1];
	strcpy(str, s.str);
	++num;
}
String::String(const char *s)
{
	len = strlen(s);
	str = new char[len + 1];
	strcpy(str, s);
	++num;
}
String::~String()
{
	cout << "Target is release!\n";
	delete[] str;
	--num;
}

 String& String::operator=(const char *s)
{
	 delete[]str;
	 len = strlen(s);
	 str = new char[len + 1];
	 strcpy(str, s);
	 return *this;
}

 String& String::operator=(const String &s)
 {
	 delete[] str;
	 len = s.len;
	 str = new char[len + 1];
	 strcpy(str, s.str);
	 return *this;
 }

 char& String::operator[](const int i)//因为返回char引用，因此可以str[i]='c'采用赋值去改变
 {
	 return str[i];
 }

 const char& String::operator[](const int i) const
 {
	 return str[i];
 }

 bool operator>(const String &str1, const String &str2)
 {
    
	 return strcmp(str1.str, str2.str)>0;
 }

 bool operator<(const String &str1, const String &str2)
 {
	 return !(str1>str2);
 }

 bool operator==(const String &str1, const String &str2)
 {
	 return strcmp(str1.str, str2.str) == 0;
 }

 String operator+(const String &str1, const String &str2)
 {
	 String temp;
	 temp.len = str1.len + str2.len + 1;
	 temp.str = new char[temp.len + 1];
	 strcpy(temp.str, str1.str);
	 strcat(temp.str, str2.str);
	 return temp;
 }

 ostream & operator<<(ostream &os, const String &str1)
 {
	 os <<"*******"<< str1.str << "********"<<endl;
	 return os;
 }

 istream& operator>>(istream &is, String &str1)
 {
	 is.getline(str1.str, MAXSIZE);
	 str1.len = strlen(str1.str);
	 return is;
 }

//main.cpp
/**
*Copyright U+00A9 2018 XXXXXX. All Right Reserved.
*Filename:
*Author:XXXXXX
*Date:2018.12.01
*Version:VS 2013
*Description:
**/

#include<iostream>
//#include<cstdlib>
#include"statement.h"

using namespace std;
int main()
{
		String str1 = "Hello,I'm a student";
		String str2 = String("OK! I agree your comments");
		cout << "str1=" << str1 << "str2=" << str2;
		str1 = "I'm a chinese";
		cout << "str1 = \"I'm a chinese\",str1=" << str1;
		String str3;
		cout << "please input a string for str3(MAXSIZE=100):" << endl;
		cin >> str3;
		cout << "str3=" << str3 << " ,*********its length=" << str3.get_len() << "**********\n";
		String str4 = str1 + str2;
		cout << "str1 + str2=str4=" << str4 << " ,*********its length=" << str4.get_len() << "**********\n";
		cout << "output the greater between str1 and str2 is:" << endl;
		if (str1 < str2) cout << "The greater is " << str2;
		else cout << "The greater is " << str1;
		String str5;
		cout << "please input a string for str5(MAXSIZE=100):" << endl;
		cin >> str5;
		cout << "The 2-th element of str5 is " << str5[1] << endl;
		str5[3] = '#';
		cout << "str5[3] = '#'=> " << str5;
		const String str6 = "I'm a student in NUAA";
		cout << "The 3-th element of " << str6 << " is " << str6[2] << endl;
	system("pause");
  return 0;
}

对于数据成员含有指针的类，采用默认构造函数时只是按值进行赋值，这样将会使得被赋值的对象数据成员存取的是赋值对象的地址，因此，应当显式的构造复制构造函数去解决深度赋值问题。

程序运行结果