srting的类构造函数、析构函数、拷贝构造函数与赋值构造函数

#pragma once

#include <iostream>
#include <string>
#include <cassert>
#include <iomanip>
using namespace std;

//自己写函数 http://blog.youkuaiyun.com/herveyhuang/article/details/39755991
unsigned int mystrlen(const char* str);
char* mystrcat(char* dest,const char* src);
char* mystrchr(char* str,char c);
int mystrcmp(const char* str1,const char* str2);
char* mystrcpy(char* dest,const char* src);
unsigned int mystrcspn ( const char * str1, const char * str2 );
char* mystrncat(char* dest,const char* src,unsigned int num);
int mystrncmp(const char* str1,const char* str2,unsigned int num);
char* mystrncpy(char* dest,const char* src,unsigned int num);
char* mystrpbrk(char* str1,char* str2);
char* mystrrchr(char* str,char c);
unsigned int mystrspn(char* str1,char* str2);
char* mystrstr(char* str,char* strSearch);



class MyString{

	friend ostream& operator <<(ostream&,MyString&); 
	friend istream& operator >>(istream&,MyString&);

public:
	MyString(const char* str = NULL);
	//assignment constructor 
	MyString(const MyString& str); 
	~MyString(){
		delete [] m_data;
	}

	//get the length of string
	int size(){
		return mystrlen(m_data);
	}
	//return substring  这里存在一些问题待改善
	//当字符串的长度稍大一些时会出错;
	MyString substr(int pos);
	MyString substr(int pos,int len);
	//overload  operator =
	MyString& operator =(const MyString& other);
	//overload operator +
	MyString operator +(const MyString& other)const;
	//overload operator +=
	MyString& operator +=(const MyString& other);
	//overload operator ==
	bool operator ==(const MyString& other)const;
	//overload operator []
	char& operator [](unsigned int);

private:
	char* m_data;
};

#include "MyString.h"



MyString::MyString(const char* str /* = NULL */)
{
	if (!str)
	{
		m_data = new char[1];
		*m_data = '\0';
	} 
	else
	{
		int nLen = mystrlen(str);
		m_data = new char[nLen + 1];
		mystrcpy(m_data,str);
	} 
}

MyString::MyString(const MyString& str)
{
	
	m_data = new char[mystrlen(str.m_data)+1];
	mystrcpy(m_data,str.m_data);
}

ostream& operator <<(ostream& oscout,MyString& str)
{
	oscout<<str.m_data;
	return oscout;
}

istream& operator >>(istream& iscin,MyString& str)
{
	char temp[255];
	iscin>>setw(255)>>temp;
	str = temp;
	return iscin;
}

MyString MyString::substr(int pos)
{
	/*
	int nLen = mystrlen(m_data);
	char* res = new char(nLen - pos +1);
	char* src = m_data + pos;
	mystrncpy(res,src,nLen-pos);
	MyString strres(res);
	return strres;
	*/

	int nLen = mystrlen(m_data);
	if (nLen < pos)
	{
		pos = nLen;
	}
	int nCopyLen = nLen - pos;
	char* res = new char(nLen - pos +1);
	char* dest =  res;
	char* src = m_data + pos;

	for (int i = 0;i < nCopyLen; i++)
	{
		*dest++ = *src++;
	}

	*dest = '\0';
	MyString strres(res);
	return strres;
}

MyString MyString::substr(int pos,int len)
{
	int maxlen = mystrlen(m_data)-pos;
	int newLen = maxlen < len ? maxlen : len;
	char* res = new char(newLen+1);
	char* src = m_data + pos;
	mystrncpy(res,src,newLen);
	MyString strres(res);
	return strres;
}

MyString MyString::operator +(const MyString& other)const
{
	MyString newString;  
	if(!other.m_data)  
		newString = *this;  
	else if(!m_data)  
		newString = other;  
	else  
	{  
		newString.m_data = new char[mystrlen(m_data)+mystrlen(other.m_data)+1];  
		mystrcpy(newString.m_data,m_data);  
		mystrcat(newString.m_data,other.m_data);  
	}  
	return newString; 
}

MyString& MyString::operator =(const MyString& other)
{
	if (this!=&other)  
	{  
		delete [] m_data;  
		if(!other.m_data)
		{
			m_data = new char[1];
			*m_data = '\0'; 
		}
		else  
		{  
			m_data = new char[strlen(other.m_data)+1];  
			mystrcpy(m_data,other.m_data);  
		}  
	}  
	return *this;
}

MyString& MyString::operator +=(const MyString& other)
{
	if (!other.m_data)
	{
		return *this;
	} 
	else
	{
		char* data = new char[mystrlen(m_data)+mystrlen(other.m_data)+1];
		mystrcpy(data,m_data);
		delete [] m_data;
		m_data = data;
		mystrcat(m_data,other.m_data);
	}
	return *this;
}

//overload operator ==
bool MyString::operator ==(const MyString& other)const
{
	if ( mystrlen(other.m_data) != mystrlen(m_data) )  
		return false;  
	return mystrcmp(m_data,other.m_data)?false:true; 
}
//overload operator []
char& MyString::operator [](unsigned int index)
{
	if (index >= 0 && index <= mystrlen(m_data))  
		return m_data[index];

	return m_data[mystrlen(m_data)+1];
}

自己写了一下string类的一些函数，这里看起来很简单的东西，费了好长时间啊，还有一点就是其中一个函数存在问题，带改善

	//return substring  这里存在一些问题待改善
	//当字符串的长度稍大一些时会出错;
	MyString substr(int pos);
	MyString substr(int pos,int len);