c++运算符重载

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#include<iostream>#include<cstring>#include<windows.h>using std::cin;using std::cout;using std::endl;using std::ostream;using std::istream;class String{public:String(){p=NULL;}String(const String &);String(char *str);~String();String & operator=(const  String &);String operator+(const String &);friend bool operator>(String &string1,String &string2);friend bool operator< (String &string1, String &string2);friend bool operator== (String &string1, String &string2);friend bool operator!= (String &string1, String &string2);friend ostream& operator << (ostream&,const String&); friend istream& operator >> (istream&,String&); void display();private:char *p;};String::String(const String &s){if(s.p)  p=new char[strlen(s.p)+1]; else p=0;  strcpy(p,s.p); } String::String(char  *str){ p=str;}String::~String(){if(p!=NULL)delete p;p=NULL;}String& String::operator=(const String &s){if(p){delete[]p; p=new char[strlen(s.p)+1];}else p=new char[strlen(s.p)+1];strcpy(p,s.p); return *this;}String String::operator +(const String &s){ String temp; if(temp.p!=NULL) delete[]temp.p; temp.p = new char[strlen(p)+strlen(s.p)+1]; strcpy(temp.p,p); strcat(temp.p,s.p); return temp;}bool operator>(String &string1,String &string2){ if(strcmp(string1.p,string2.p)>0) return true; else return false;}bool operator<(String &string1,String &string2){ if(!operator>(string1,string2)) return true; else return false;}bool operator==(String &string1,String &string2){ if(strcmp(string1.p,string2.p)==0) return true;  else return false;}bool operator !=(String &string1, String &string2){ if(!(string1.p==string2.p)) return true; else return false;}ostream& operator <<(ostream &output,const String &s){ output<<s.p; return output;}istream& operator >>(istream &intput,String &s){ //cout<<"input a string:";char temp[100000] = {"",};intput>>temp;s.p=temp; return intput;}void String::display(){ cout<<p<<endl;}void compare(String &string1,String &string2){if(operator>(string1,string2)==1)    {cout<<"string1>string2"<<endl;}elseif(operator<(string1,string2)==1){cout<<"string1<string2"<<endl;}if(operator==(string1,string2)==1){cout<<"string1=string2<<endl";}if(operator==(string1,string2)!=1){cout<<"string1!=string2"<<endl;}}int main(){String string1("Hello"),string2("World");cout<<"输出string1:";string1.display();cout<<"输出string2:";string2.display();cout<<"比较string1和string2:";compare(string1,string2);String string4,string5,string6;cout<<"string1和string2连接后赋值给string4:"<<endl;string4=string1+string2;string4.display();cout<<"输入string5:";cin>>string5; cout<<"输出string5:"<<endl;cout<<string5<<endl;cout<<"string1赋值给string6:"<<endl;string6=string1;string6.display();system("pause");return 0;}
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