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.各种运算符的重载

/*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;elsereturn 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;elsereturn 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;}elsecout<<"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;}

2.String 类构造函数，拷贝构造函数，析构函数的调用

#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 StringString s2;s2=s1;//Create String  Create String assign String   delete String   delete String(深赋值)}

3.引用计数模型的String 类

#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;}