String 类的编写：1.各种运算符的重载 2.用引用计数来实现String类

/*1.String 类的编写(主要是写运算符+  +=  -  >  <  >=  <=的重载)：
#include<iostream>
using namespace std;
class String;
ostream& operator<<(ostream &out,const String &s);
class String
{
friend ostream& operator<<(ostream &out,const String &s);
public:
String(const char *str="")
{
if(str==NULL)
{
data=new char[1];
data[0]='\0';
}
else
{
data=new char[strlen(str)+1];
strcpy(data,str);
}
}
String(const String &s)
{
data=new char(strlen(s.data)+1);
strcpy(data,s.data);
}
String& operator=(const String &s)//深赋值
{
if(this!=&s)
{
delete[]data;//1.释放原有空间
data=new char[strlen(s.data)+1];//2.开辟新空间
strcpy(data,s.data);//3.进行拷贝

}
return *this;//4.返回*this
}
~String()
{

delete[]data;
data=NULL;

}
public:
String operator+(const String &s)
{
int len;
char *str=NULL;
len=strlen(data)+strlen(s.data)+1;
str=new char[len];
strcpy(str,data);
strcat(str,s.data);
return String(str);

}
/*String operator-(const String &s)
{
int i=0;
int len;
char *str1,*str2;
char *str=NULL;
str1=data;
str2=s.data;
len=strlen(data)-strlen(s.data)+1;
str=new char[len];
while(*str1!='\0')
{
if(*str1==*str2)
{
str1++;
str2++;
}
else
{
str[i++]=*str1;
str1++;
}
}
str[len-1]='\0';//必须写，如果不写后面就是乱码
return String(str);
}
String& operator+=(const String &s)
{
char *str;
str=new char[strlen(data)+strlen(s.data)+1];
strcpy(str,data);
delete []data;
strcat(str,s.data);
data=str;
return *this;

}

bool operator>(const String &s)
{
int n1=strlen(data);
int n2=strlen(s.data);
if(n1>n2)
return true;
else if(n1<n2)
return false;
else
{
char *str1=data;
char *str2=s.data;
while(*str1!='\0'&&*str2!='\0')
{
if(*str1>*str2)
{
return true;
}
str1++;
str2++;
}
if(*str1=='\0'&&*str2=='\0')
return false;

}

}

bool operator<(const String &s)
{
int n1=strlen(data);
int n2=strlen(s.data);
if(n1<n2)
return true;
else if(n1>n2)
return false;
else
{
char *str1=data;
char *str2=s.data;
while(*str1!='\0'&&*str2!='\0')
{
if(*str1<*str2)
{
return true;
}
str1++;
str2++;
}
if(*str1=='\0'&&*str2=='\0')
return false;

}

}
bool operator>=(const String &s)
{
int n1=strlen(data);
int n2=strlen(s.data);
if(n1>n2)
return true;
else if(n1<n2)
return false;
else
{
char *str1=data;
char *str2=s.data;
while(*str1!='\0'&&*str2!='\0'&&*str1==*str2)
{
str1++;
str2++;
}
if(*str1=='\0'&&*str2=='\0')
return true;
else
return false;

}

}
bool operator<=(const String &s)
{
int n1=strlen(data);
int n2=strlen(s.data);
if(n1<n2)
return true;
else if(n1>n2)
return false;
else
{
char *str1=data;
char *str2=s.data;
while(*str1!='\0'&&*str2!='\0'&&*str1==*str2)
{
str1++;
str2++;
}
if(*str1=='\0'&&*str2=='\0')
return true;
else
return false;

}

}

bool operator==(const String &s)
{
char *str1=data;
char *str2=s.data;
while(*str1!=NULL&&*str2!=NULL&&*str1==*str2)
{
str1++;
str2++;
}
if(*str1=='\0'&&*str2=='\0')
return true;
else
return false;
}
bool operator!=(const String &s)
{
char *str1=data;
char *str2=s.data;
while(*str1!='\0'&&*str2!='\0'&&*str1==*str2)
{
str1++;
str2++;
}
if(*str1=='\0'&&*str2=='\0')
return false;
else
return true;

}
private:
char *data;

};
int main()
{
//String s1("abc");
//String s2("123");
//cout<<"s1+s2="<<s1+s2;
String s1("eefe");
String s2("fefe");
/*if(s1!=s2)
{
cout<<"不相等"<<endl;
}
else
{
cout<<"相等"<<endl;

}*/
/*
if(s1==s2)
{
cout<<"相等"<<endl;
}
else
{
cout<<"不相等"<<endl;
}

if(s1>s2)
{
cout<<"大于"<<endl;
}
else
{
cout<<"不大于"<<endl;
}*/
//cout<<"s1-s2="<<s1-s2;

/*
if(s1<s2)
{
cout<<"小于"<<endl;
}
else
{
cout<<"不小于"<<endl;
}*/
/*
if(s1>=s2)
{
cout<<"符合大于等于"<<endl;
}
else
cout<<"不符合大于等于"<<endl;
return 0;*/
/*
if(s1<=s2)
{
cout<<"符合小于等于"<<endl;
}
else
{
cout<<"不符合小于等于"<<endl;
}

s1+=s2;
cout<<s1<<endl;
}
ostream& operator<<(ostream &out,const String &s)
{
out<<s.data;
return out;
}

#include<iostream>
using namespace std;
class String;
ostream& operator<<(ostream& out,const  String  &s);
class String
{
friend ostream& operator<<(ostream& out,const  String   &s);
public:
String(const char *str="")
{
if(str==NULL)
{
data=new char[1];
data[0]='\0';
}
else
{
data=new char[strlen(str)+1];
strcpy(data,str);
}
cout<<"Create String"<<endl;

}
String(const String &s)
{
data=new char[strlen(s.data)+1];
strcpy(data,s.data);
cout<<"Copy String"<<endl;

}
String& operator=(const String &s)
{
if(this!=&s)
{
delete[]data;//深赋值
data=new char[strlen(s.data)+1];
strcpy(data,s.data);
}
cout<<"assign String"<<endl;
return *this;
}
~String()
{
delete[]data;
data=NULL;
cout<<"delete String"<<endl;
}
private:
char *data;

};
ostream& operator<<(ostream &out,const String &s)
{
out<<s.data;
return out;
}
void main()
{
String s1("abc");//Create String  delete String
//String s2=s1;//Create String  Copy String(调拷贝构造函数)  delete String delete String
String s2;
s2=s1;//Create String  Create String assign String   delete String   delete String(深赋值)
}

#include<iostream>
using namespace std;
class String;
ostream& operator<<(ostream& out,String &s);
class String_rep
{
friend class String;
friend ostream& operator<<(ostream& out,String &s);
public:
String_rep(const char *str=""):use_count(0)
{
if(str==NULL)
{
data=new char[1];
data[0]='\0';
}
else
{
data=new char[strlen(str)+1];
strcpy(data,str);
}

}
String_rep(const String_rep &s);
String_rep& operator=(const String_rep &s);

~String_rep()
{
delete[]data;
data=NULL;
}
public:
void increment()
{
++use_count;
}
void decrement()
{
if(--use_count==0)
{
delete this;
}
}
private:
char *data;
int use_count;
};
ostream& operator<<(ostream& out,String &s);
class String
{
friend ostream& operator<<(ostream& out,String &s);
public:
String(const char *str=""):rep(new String_rep(str))
{
rep->increment();

}
String(const String &s)
{
rep=s.rep;
rep->increment();

}
String& operator=(const String &s)
{
if(this!=&s)
{
rep->decrement();
rep=s.rep;
rep->increment();
}
return *this;

}
~String()
{
rep->decrement();
}
public:
void upper()//转换大小写函数
{
String_rep *new_rep=new String_rep(rep->data);
rep->decrement();
rep=new_rep;
new_rep->increment();
char *p=rep->data;
while(*p!='\0')
{
*p-=32;
++p;
}

}
private:
String_rep *rep;
};
void main()
{
String s1("abc");
String s2=s1;

String s3;
s3=s2;

s1.upper();
cout<<"s1="<<s1<<endl;
cout<<"s2="<<s2<<endl;
cout<<"s3="<<s3<<endl;

}
ostream& operator<<(ostream& out,String &s)
{
out<<s.rep->data;
return out;

}