C++中sting类的简单实现方法

class String 
{ 
friend ostream &operator<<(ostream &os,String &s); 
public: 
String(const char *str=""); //全缺省的构造函数，解决空字符串的问题 
String(const String &ps); //深拷贝 
String &operator=(String s); 
String &operator+=(const char * s); 
const char *C_Str()const //得到C风格的字符指针 
{ 
return _pstr; 
} 
char &operator[](size_t index) 
{ 
return _pstr[index]; 
} 
size_t Size()const 
{ 
return _size; 
} 
void PushBack(char c); 
String &Insert(size_t pos,const char *str); 
//String &operator=(String &s) 
//{ 
// cout<<"String &operator=(String &s)"<<endl; 
// if(this != &s) 
// { 
// delete[]_pstr; 
// _pstr=new char[strlen(s._pstr)+1]; 
// strcpy(_pstr,s._pstr); 
// } 
// return *this; 
//} 
~String() 
{ 
cout<<"~String()"<<endl; 
if(_pstr != NULL) 
{ 
delete[]_pstr; 
_pstr=NULL; 
_size=0; 
_capacity=0; 
} 
} 
private: 
void CheckCapacity(int count); 
private: 
int _size; 
int _capacity; 
char *_pstr; 
}; 
ostream &operator<<(ostream &os,String &s) 
{ 
os<<s._pstr; 
return os; 
} 
String::String(const char *str) 
:_size(strlen(str)) 
,_capacity(strlen(str)+1) 
,_pstr(new char[_capacity]) 
{ 
cout<<"String()"<<endl; 
strcpy(_pstr,str); 
} 
String::String(const String &ps) 
:_size(ps._size) 
,_capacity(strlen(ps._pstr)+1) 
,_pstr(new char[_capacity]) 
{ 
cout<<"String(const String &ps)"<<endl; 
strcpy(_pstr,ps._pstr); 
} 
String &String::operator=(String s) 
{ 
cout<<"String &operator=(String s)"<<endl; 
std::swap(_pstr,s._pstr); 
std::swap(_size,s._size); 
std::swap(_capacity,s._capacity); 
return *this; 
} 
void String::CheckCapacity(int count) 
{ 
if(_size+count >= _capacity) 
{ 
int _count=(2*_capacity)>(_capacity+count)?(2*_capacity):(_capacity+count); 
char *tmp=new char[_count]; 
strcpy(tmp,_pstr); 
delete[]_pstr; 
_pstr=tmp; 
_capacity=_count; 
} 
} 
void String::PushBack(char c) 
{ 
CheckCapacity(1); 
_pstr[_size++]=c; 
_pstr[_size]='\0'; 
} 
String &String::operator+=(const char * s) 
{ 
CheckCapacity(strlen(s)); 
while(*s) 
{ 
_pstr[_size++]=*s; 
s++; 
} 
_pstr[_size]='\0'; 
return *this; 
} 
String &String::Insert(size_t pos,const char *str) 
{ 
char *tmp=new char[strlen(_pstr+pos)]; 
strcpy(tmp,_pstr+pos); 
CheckCapacity(strlen(str)); 
while(*str) 
{ 
_pstr[pos++]=*str; 
str++; 
} 
strcpy(_pstr+pos,tmp); 
return *this; 
}

void text1() 
{ 
String str1("hello"); 
String str2(str1); 
String str3; 
str3=str1; 
cout<<str1<<endl; 
cout<<str2<<endl; 
cout<<str3<<endl; 
cout<<strlen(str1.C_Str())<<endl; //5 
str1[4]='w'; 
cout<<str1<<endl; //hellw 
} 
void text2() 
{ 
String str1("abcd"); 
cout<<str1<<endl; 
str1.PushBack('e'); 
str1.PushBack('f'); 
str1.PushBack('g'); 
str1.PushBack('h'); 
str1.PushBack('i'); 
cout<<str1<<endl; 
cout<<str1.Size()<<endl; 
} 
void text3() 
{ 
String str1("hello"); 
String str2("hello world"); 
String str3(str2); 
str1+=" "; 
str1+="world"; 
cout<<str1<<endl; 
str2.Insert(6," abc "); 
cout<<str2<<endl; 
}

//写时拷贝的方式 
class String 
{ 
friend ostream& operator<<(ostream & os,String &s); 
public: 
String(const char *str="") 
:_str(new char[strlen(str)+1+4]) 
{ 
cout<<"构造"<<endl; 
_str+=4; 
*((int *)(_str-4))=1; 
strcpy(_str,str); 
} 
String(String &s) 
{ 
cout<<"拷贝构造"<<endl; 
++*((int *)(s._str-4)); 
_str=s._str; 
} 
String &operator=(const String &s) 
{ 
cout<<"赋值语句"<<endl; 
if(--*(int *)(_str-4) == 0) 
{ 
delete[](_str-4); 
} 
++(*(int *)(s._str-4)); 
_str=s._str; 
return *this; 
} 
char &operator[](int index) //写时拷贝 
{ 
assert(index >= 0 && index < (int)strlen(_str)); 
if(*(int *)(_str-4) > 1) 
{ 
--*(int *)(_str-4); 
char *tmp=new char[strlen(_str)+5]; 
strcpy(tmp+4,_str); 
delete[](_str-4); 
_str=tmp+4; 
*(int *)(_str-4)=1; 
} 
return _str[index]; 
} 
~String() 
{ 
cout<<"析构"<<endl; 
if(--*(int *)(_str-4) == 0) 
{ 
cout<<"释放"<<endl; 
delete[](_str-4); 
} 
} 
private: 
char *_str; 
}; 
ostream& operator<<(ostream &os,String &s) 
{ 
os<<s._str; 
return os; 
}

void test1() 
{ 
String str1("abcd"); 
cout<<str1<<endl; 
String str2(str1); 
cout<<str2<<endl; 
String str3; 
str3=str1; 
cout<<str3<<endl; 
} 
void test2() 
{ 
String str1("abcd"); 
cout<<str1<<endl; 
String str2; 
str2=str1; 
cout<<str2<<endl; 
str2[2]='w'; 
cout<<str2<<endl; 
}