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#include <iostream>
#include<stdlib.h>
#include<stdio.h>
#include<sstream>
#include<string.h>
using namespace std;
class String
{
private:
char *pstr_;
public:
String();
String(const char *);
String(const String&);
~String();
String & operator = (const String &);
String & operator = (const char *);
String & operator += (const String &);
String & operator += (const char *);
char & operator [] (std::size_t index);
const char & operator [](std::size_t index)const;
std::size_t size() const;
const char* c_str() const;
friend bool operator == (const String &,const String &);
friend bool operator != (const String &,const String &);
friend bool operator < (const String &,const String &);
friend bool operator > (const String &,const String &);
friend bool operator <= (const String &,const String &);
friend bool operator >= (const String &,const String &);
friend std::ostream & operator << (std::ostream & os,const String &s);
friend std::istream & operator >> (std::istream & is,String & s);
};
String operator + (const String &,const String &);
String operator + (const String &,const char *);
String operator + (const char *,const String &);
String::String()
{
cout<<"String()"<<endl;
pstr_=new char[1];
strcpy(pstr_,"");
}
String::~String()
{
cout<<"~String()"<<endl;
delete []pstr_;
}
String::String(const char *str)
{
cout<<"String(const char *)"<<endl;
pstr_=new char[strlen(str)+1];
strcpy(pstr_,str);
}
String :: String(const String & s)
{
cout<<"String(const String &)"<<endl;
pstr_=new char[strlen(s.pstr_)+1];
strcpy(pstr_,s.pstr_);
}
String & String::operator = (const String & s)
{
cout<<"String & operator =(const String &)"<<endl;
this->~String();
pstr_=new char[strlen(s.pstr_)+1];
strcpy(pstr_,s.pstr_);
return *this;
}
String & String::operator =(const char *s)
{
cout<<"String & operator=(const char *)"<<endl;
this->~String();
pstr_=new char[strlen(s)+1];
strcpy(pstr_,s);
return *this;
}
String & String::operator +=(const String &s)
{
cout<<"String & operator += (const String &)"<<endl;
int len1=strlen(this->pstr_);
int len2=strlen(s.pstr_);
char *a=(char*)calloc(len1,sizeof(char));
strcpy(a,this->pstr_);
this->~String();
this->pstr_=new char[len1+len2+1];
sprintf(this->pstr_,"%s%s",a,s.pstr_);
return *this;
}
String & String::operator += (const char *s)
{
cout<<"String & operator += (const char *)"<<endl;
int len1=strlen(this->pstr_);
int len2=strlen(s);
char *a=(char*)calloc(len1,sizeof(char));
strcpy(a,this->pstr_);
this->~String();
this->pstr_=new char[len1+len2+1];
sprintf(this->pstr_,"%s%s",a,s);
return *this;
}
std::ostream & operator<<(std::ostream & os,const String &s)
{
cout<<"std::ostream & operator << (std::ostream & ,const String &)"<<endl;
os<<s.pstr_;
return os;
}
char& String::operator[] (std::size_t index)
{
cout<<"char & operator[] (std:: size_t index)"<<endl;
int len=strlen(this->pstr_);
char *a=(char*)calloc(len,sizeof(char));
strcpy(a,pstr_);
return a[index];
}
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const char& String::operator[](std::size_t index)const
{
cout<<"const char & operator[] (std:: size_t index)const"<<endl;
int len=strlen(this->pstr_+1);
//This is wrong, this->pstr_+1 is equivalent to correcting the offset to the next character
char *a=(char*)calloc(len,sizeof(char));
strcpy(a,pstr_);
return a[index];
}
std::size_t String::size()const
{
cout<<"std::size_t size()const"<<endl;
int len=strlen(this->pstr_);
return len;
}
const char* String::c_str() const
{
cout<<"const char* c_str() const"<<endl;
int len=strlen(this->pstr_+1);
char *a=(char*)calloc(len,sizeof(char));
//No matter how much space is applied here, if the later copy function is not enough, he will automatically apply for space, so there is no error in the result
strcpy(a,pstr_);
return a;
}
bool operator == (const String & a1,const String &a2)
{
cout<<"bool operator == (const String &,const String &)"<<endl;
if((strcmp(a1.c_str(),a2.c_str()))==0)
return 1;
return 0;
}
bool operator != (const String & a1,const String & a2)
{
cout<<"bool operator != (const String &,const String &)"<<endl;
if((strcmp(a1.c_str(),a2.c_str()))!=0)
return 1;
return 0;
}
bool operator < (const String &a1,const String &a2)
{
cout<<"bool operator < (const String &,const String &)"<<endl;
if((strcmp(a1.c_str(),a2.c_str()))<0)
return 1;
return 0;
}
bool operator > (const String &a1,const String &a2)
{
cout<<"bool operator > (const String &,const String &)"<<endl;
if((strcmp(a1.c_str(),a2.c_str()))>0)
return 1;
return 0;
}
bool operator <= (const String &a1,const String &a2)
{
cout<<"bool operator <= (const String &,const String &)"<<endl;
if((strcmp(a1.c_str(),a2.c_str()))<0)
return 1;
else if((strcmp(a1.c_str(),a2.c_str()))==0)
return 1;
return 0;
}
bool operator >= (const String &a1,const String &a2)
{
cout<<"bool operator >= (const String &,const String &)"<<endl;
if((strcmp(a1.c_str(),a2.c_str()))>0)
return 1;
else if((strcmp(a1.c_str(),a2.c_str()))==0)
return 1;
return 0;
}
std::istream & operator >> (std::istream & is,String &s)
{
cout<<"std::istream & operator >> (std::istream &m,String &)"<<endl;
is>>s.pstr_;
return is;
}
String operator + (const String &a1,const String &a2)
{
cout<<"String operator + (const String &,const String &)"<<endl;
String tmp=a1;
tmp+=a2;
return tmp;
}
String operator + (const String &a1,const char * a2)
{
cout<<"String operator + (const String &,const char *)"<<endl;
String tmp=a1;
tmp+=a2;
return tmp;
}
String operator + (const char *a1,const String & a2)
{
cout<<"String operator + (const char *,const String &)"<<endl;
String tmp;
tmp+=a1;
tmp+=a2;
return tmp;
}
//测试代码
int main()
{
String s;
String s1("hello");
String s2(s1);
String s3="world";
s1=s2;
String s4;
s4="wangdao";
s+=s3;
s4+="nihao";
cout<<s4<<endl;
cout<<s4[2]<<endl;
cout<<s4.size()<<endl;
cout<<s4.c_str()<<endl;
bool bool1=(s1>s4);
cout<<bool1<<endl;
bool bool2=(s1>=s3);
cout<<bool2<<endl;
cin>>s;
cout<<s<<endl;
String s5=s1+s2;
cout<<s5<<endl;
String s6=s1+"shenzhen";
cout<<s6<<endl;
String s7="shenzhen1"+s1;
cout<<s7<<endl;
return 0;
}
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String class operator overloading, implement it yourself
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