学步园

1：MyString.h

#pragma once
class myCString
{
public:
	int GetLength()const {return m_nLength;}

	myCString(void);//无参构造函数
	myCString(const char* p);//根据字符串常量初始化
	myCString(const myCString& rhs);//拷贝构造
	myCString(char ch,int nRepeat = 1);//串内有n个ch字符
	myCString(const char* cstr, int nLength);//根据字符串常量的一部分进行构造


	operator const char* (){return m_pDate;}//类型转换函数


public:
	char operator[](int nIndex) const;//获取串内上的某个字符
	myCString& operator = (const char* cstr);
	myCString& operator = (const myCString& str);
	myCString& operator +=(const char* p);
	myCString& operator +=(const myCString& str);

public:

	myCString operator+(  const char* pszSrc) const;	//来源不改变，返回一个对象
	myCString operator+(  const myCString& str) const;	//来源不改变，返回一个对象

	friend bool operator!=(const myCString& str1,const myCString& str2);
	friend bool operator==(const myCString& str1,const myCString& str2);
	friend bool operator< (const myCString& str1, const myCString& str2);
	friend bool operator> (const myCString& str1, const myCString& str2);



	~myCString(void);

private:
	int  m_nLength;
	char* m_pDate;

};

MyString.cpp

#include "stdafx.h"
#include "myCString.h"
#include <string.h>
#include <iostream>
using namespace std;

myCString::myCString(void)
{
	m_pDate = new char(0);
	m_nLength = 0;
}

myCString::myCString(const char* p)
{
	if (p == NULL)
	{
		m_pDate = new char[1];
		*m_pDate = '\0';
	}
	m_nLength = strlen(p);
	m_pDate = new char[m_nLength+1];
	strcpy(m_pDate,p);

}

myCString::myCString(const myCString& rhs)
{
	m_nLength = rhs.m_nLength;
	m_pDate   = new char[m_nLength+1];
	strcpy(m_pDate,rhs.m_pDate);
}


myCString::myCString(char ch,int nRepeat)//串内有n个ch字符
{
	m_nLength = nRepeat;
	m_pDate   = new char[m_nLength + 1];
	for (int i = 0; i < m_nLength; i++)
	{
		m_pDate[i] = ch;
	}
	m_pDate[m_nLength] = '\0';

}
myCString::myCString(const char* cstr, int nLength)//根据字符串常量的一部分进行构造
{
	m_nLength = strlen(cstr);
	m_nLength = m_nLength<nLength? m_nLength:nLength;//在cstr字符串的长度和 输入的nLength中选择比较小的

	m_pDate   = new char[m_nLength+1];
	for(int i = 0; i < m_nLength; i++)
	{
		m_pDate[i] = cstr[i];
	}
	m_pDate[m_nLength] = '\n';
}

char myCString::operator[](int nIndex) const
{
	return m_pDate[nIndex];
}

myCString& myCString::operator = (const char* cstr)
{
	char* mOldp = m_pDate;//保存旧的指针 effective C++  条款11
	m_nLength = strlen(cstr);
	m_pDate   = new char[m_nLength+1];//分配多一个字节存放\0；
	strcpy(m_pDate,cstr);
	delete mOldp;
	return *this;

}
myCString& myCString::operator = (const myCString& str)
{
	//不加if里面的也可以，但是加上效率高一点，因为如果str的长度小于原来的长度，那么就不用重新申请空间了。
	if (m_nLength > str.m_nLength)
	{
		strcpy(m_pDate,str.m_pDate);
	}
	else
	{
		char* mOldp = m_pDate;
		m_nLength   = str.GetLength();
		m_pDate		= new char[m_nLength+1];
		strcpy(m_pDate,str.m_pDate);
		delete mOldp;
		return* this;
	}
	
}


/*  //可能出现内存泄漏
myCString& myCString::operator +=(const char* p)
{
	m_nLength = m_nLength+strlen(p);
	char* pNew = new char[m_nLength+1];
	strcpy(pNew,m_pDate);
	strcat(pNew,p);
	delete []m_pDate;
	m_pDate = pNew;

	return *this;
}
*/

myCString& myCString::operator +=(const char* p)
{
	char* pOld = m_pDate;
	m_nLength = m_nLength+strlen(p);
	char* pNew = new char[m_nLength+1];
	strcpy(pNew,m_pDate);
	strcat(pNew,p);
	m_pDate = pNew;
	delete pOld;

	return *this;
}

myCString& myCString::operator +=(const myCString& str)
{
	char* pOld = m_pDate;
	m_nLength = m_nLength + str.m_nLength;//str.GetLength();//这里刚开始以为str不能直接访问a，
	//结果也可以，大吃一惊啊，原来只要是成员函数当中的类对象就可以访问私有成员。
	char* pNew = new char[m_nLength+1];
	strcpy(pNew,m_pDate);
	strcat(pNew,str.m_pDate);
	m_pDate = pNew;
	delete pOld;

	return *this;
}

//怀疑pszSrc是其他的myCString对象，不是this的对象不能调用其私有成员？？
//应该是可以调用的，因为只要调用位置是myCString类的成员函数就够了。
myCString myCString::operator+(  const char* pszSrc)const	//来源不改变，返回一个对象
{
	myCString rec;
	rec.m_nLength = m_nLength +strlen(pszSrc);
	rec.m_pDate = new char[m_nLength+1];
	strcpy(rec.m_pDate,m_pDate);
	strcat(rec.m_pDate,pszSrc);

	return rec;


}

//只读函数：让this指针变为了const myString*类型
//非只读函数：this指针 原本是myString* 类型
//friend CString operator +( const CString& string1, const CString& string2 );
//只读函数后面的const与全局函数中左值前面的const达到的效果相同
myCString myCString::operator+(  const myCString& str) const	//来源不改变，返回一个对象
{
	myCString rec;
	delete []rec.m_pDate;
	rec.m_nLength = m_nLength+str.m_nLength;
	rec.m_pDate  = new char[m_nLength+1];
	strcpy(rec.m_pDate,m_pDate);
	strcat(rec.m_pDate,str.m_pDate);

	return rec;
}

bool operator!=(const myCString& str1,const myCString& str2) 
 {
	 bool b = strcmp(str1.m_pDate,str2.m_pDate);
	 return b != 0;

 }

 bool operator==(const myCString& str1,const myCString& str2) 
 {
	 bool b = strcmp(str1.m_pDate,str2.m_pDate);
	 return !b;
 }
 
 bool operator<(const myCString& str1, const myCString& str2) 
 {
	 return strcmp(str1.m_pDate,str2.m_pDate)<0;
 }
 bool operator > (const myCString& str1, const myCString& str2)
 {
	 return strcmp(str1.m_pDate,str2.m_pDate)>0;
 }
 
myCString::~myCString(void)
{
	delete []m_pDate;
}

3:main.cpp

// String编写.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include "myCString.h"
#include <iostream>
#include <stdio.h>
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
	/*
	myCString str1;
	myCString str2("Hello");
	myCString str3("你是谁");
	str2 += "World";
	myCString str4 = str2;
	cout<<(const char*)str2<<endl;
	cout<<str2.GetLength()<<endl;


	char a[7]="abcdef";
	char b[4]="ABC";
	strcpy(a,b);
	for(int i=0;i<7;i++)
		printf ("%c",a[i]); //说明strcpy不是清除后再赋值
	*/

	myCString str1("Hello");
	myCString str2(str1);
	if (str2 == str1)
	{
		cout<<"相等"<<endl;
	}
	myCString str3("HH");
	if (str3 != str2)
	{
		cout<<"不相等"<<endl;
	}	
	getchar();
	return 0;
}