重载运算符实现精简版string类

c语言利用数组保存字符串，经常在不经意中浪费了大量的空间，使用起来十分的不方便，而且容易出错，为了解决c语言字符串的问题，c++增加了一个string类。本例就是为了说明通过运算符的重载而实现的。

代码如下：

#include<iostream>
using namespace std;
class String
{
public:
	String();
	~String();
	String(const String &rs);
	String(const char* const ch);
	char &operator[](unsigned short int length );
	char operator[](unsigned short int  length) const;

	String &operator=(const String &s);
	String operator+(const String &);
	void operator+=(const String &rs);

	friend ostream &operator<<(ostream & o,const String &str)
	{
		o<<str.str;
		return o;
	
		
	
	}

	friend istream &operator>>(istream &i,String str)
	{
	
		i>>str.str;
		return i;
	}

	friend bool operator<(const String &str1,const String &str2)
	{
	
		if(strcmp(str1.str,str2.str)<0)
			return 1;
		else 
			return 0;
	}

	friend bool operator>(const String &str1,const String &str2)
	{
	
		if(strcmp(str1.str,str2.str)>0)
			return 1;
		else 
			return 0;
	}

		friend bool operator==(const String &str1,const String &str2)
	{
	
		if(strcmp(str1.str,str2.str)==0)
			return 1;
		else 
			return 0;
	}

		unsigned short int getlen() const {return len;}
		const char* getstr() const{return str;}



private:
	String(unsigned short int);
	unsigned short int len;
	char *str;




};

String::String(unsigned short int length)
{

	str = new char[length + 1];
	int i;
	for(i = 0;i <length;i++)
		str[i] = '\0';
	len = length;
}

String::String()
{

	len = 0;
	str = new char[1];

	str[0] = '\0';

}

String::~String()
{

	delete []str;
	len = 0;
}

String::String(const String &rs)
{

	len = rs.getlen();
	str = new char[len + 1];
	for(int i =0 ;i < len ;i++ )
		str[i] = rs[i];
	str[len] = '\0';


}

char &String ::operator [](unsigned short int length)
{

	if(length > len)
		return str[len - 1];
	else
		return str[length];


}

char String::operator [](unsigned short int length) const
{

		if(length > len)
		return str[len - 1];
	else
		return str[length];

	

}

String &String::operator =(const String &s)
{

	if(this == &s)
	return *this;
	delete []str;
	len = s.getlen();
	str = new char[len + 1];
	for(int i=0;i<len;i++)
	{
	
		str[i] = s[i];

	}
	str[len] = '\0';

	return *this;




}

String String::operator +(const String &rs)
{

	int total = len + rs.getlen();
	String temp(total);
	int i,j;
	for( i = 0;i < len;i++)
		temp[i] = str[i];
	for(j = 0;j<rs.getlen();j++,i++)
		temp[i] = rs[j];
	temp[total] = '\0';
	
	return temp;


}

void String::operator +=(const String &rs)
{

	int total = len + rs.getlen();
	String temp(total);
	int i,j;
	for(i = 0;i < len;i++)
		temp[i] = str[i];
	for(j = 0;j < rs.getlen();j++,i++)
		temp[i] = rs[j];
	temp[total] = '\0';
	*this = temp;

}

String::String(const char* const ch)
{

	len = strlen(ch);
	str = new char[len+1];
	for(int i = 0;i < len;i++)
		str[i] = ch[i];
	str[len] = '\0';
}


int main()
{

	String s1;
	cout<<"s1的长度:"<<s1.getlen()<<endl;
	char*temp = "help me";
	s1 = temp;
	cout<<"s1: "<<s1.getstr()<<"\t s1的长度: "<<s1.getlen()<<endl;
	char ch[10];
	strcpy(ch,"all right");
	s1 += ch;
	cout<<"ch:\t"<<ch<<endl;
	cout<<"s1: \t"<<s1.getstr()<<endl;
	cout<<"s1:"<<s1<<endl;

	s1[2] = 'o';
	cout<<"s1:"<<s1<<endl;
	cout<<"s1[999]: "<<s1[999]<<endl;
	String s2 = "mother";

	String s3("Mother");
	cout<<"s2: "<<s2<<"\t s3: "<<s3<<endl;
	String s4 = s2 + s3;
	cout<<" s2 + s3 = "<<s4<<endl;
	int check = s2>s3;
	cout<<"s2>s3: "<<check<<endl;
	check = s2 < s3;
	cout<<"s2<s3: "<<check<<endl;

	check = s2 == s2;
	cout<<"s2 == s2: "<<check<<endl;
	cin>>s2[0]>>s3[0];
	s2 = s2 + s3;
	cout<<"s2: "<<" \t"<<s2<<endl;

	return 0;
}

运行的结果是：