MyString();

MyString(const MyString &str);

MyString(const char*str);

MyString &operator=(const MyString &str);    //利用已有的string对象通过=给一个对象进行赋值
MyString &operator=(const char*str);       //直接用常量字符串进行赋值

MyString &assign(const MyString&str);
MyString &assign(const char*sstr);

size_t getsize()const;                  //返回字符串大小
void clear（）；                      //把字符串清空
bool empty();                       //判断字符串是否为空
void swap(MyString &str);              //交换两个字符串
int compare(const MyString &str)const;      //比较2个字符串的大小
//第一个const说明显式调用的字符串不可更改，括号外面的const说明隐式调用的字符串不可更改，只读数据    
int compare(const char*str);           

MyString &operator+=(const MyString&str);
MyString &operator+=(const char*str);
MyString &append(const MyString&str);
MyString &append(const char *str)；

MyString substr(size_t pos = 0,n=npos) const; 

friend bool operator==(const MyString &str1,const MyString &str2);
friend bool operator==(const char *str,const MyString &str2);
friend bool operator==(const MyString &str1,const MyString *str2);
friend bool operator>(const MyString &str1,const MyString &str2);
friend bool operator>(const char*str1,const MyString &str2);
friend bool operator>(const MyString &str1,const char*str2);

friend MyString operator+(const MyString &str1,const MyString &str2);
friend MyString operator+(const char*str1,const MyString &str2);      //两个字符串进行相加
friend MyString operator+(const MyString &str1,const char*str2);

friend ostream & operator<<(ostream &os,const MyString &str);       //输出命令符的重载

char *string;                     //指向字符串的指针
int length;                       //字符串的长度
static const int string_number = 0;      //计数创建的字符串的数目

MyString::MyString() 
{ 
  length = 0; 
  string = new char; 
  char *s = "/0"; 
  memcpy(string,s,1); 
  ++string_number; 
} 
 
MyString::MyString(const char*str) 
{ 
  length = strlen(str); 
  string = new char(length+1); 
  memcpy(string,s,length); 
  ++string_number; 
} 
MyString::MyString(MyString &str) 
{ 
  length = str.length; 
  string = str.string; 
  ++string_number; 
} 
 
MyString::~MyString() 
{   
  delete[]string; 
  --string_number; 
} 

   MyString::MyString()
  {
    length = 0;
    string = new char;
    string = "/0";
    ++string_number;
  }

MyString &MyString::operator+=(const MyString&str) 
{ 
   char *dest; 
   dest = new char[str.length+length+1]; 
   memcpy(dest,string,length); 
   memcpy(dest+length,str.string,str.length+1); 
   delete[]string; 
   length = length+str.length; 
   string = dest; 
   return*this; 
} 
MyString &MyString::operator+=(const char*str) 
{ 
   char *dest; 
   dest = new char[strlen(str)+length+1]; 
   memcpy(dest,string,length); 
   memcpy(dest+length,str,strlen(str)+1); 
   delete[]string; 
   string = dest; 
   return *this; 
} 
 
 //字符串赋值 
MyString &MyString::operator=(const MyString&str) 
{ 
  if(&str == this) 
    return *this; 
  delete[]string; 
  string = new char[str.length]; 
  memcpy(string,str.string,str.length); 
  length = str.length; 
  return *this; 
} 

size_t MyString::getsize(MyString &str) 
{ 
 return strlen(str.string); 
} 
void MyString::clear() 
{ 
 length = 0; 
 while(string!='/0') 
 *string ='/0'; 
} 
bool MyString::empty() 
{ 
 return strlen(string)==0; 
} 
int MyString ::compare(const MyString &str) 
{ 
  return compare(string,str.string); 
} 
void MyString::swap(MyString &str) 
{ 
  char *temp; 
  temp = string; 
  string = str.string; 
  str = temp; 
} 
Mystring MyString::substr(sizez_t pos=0,size_t n )const 
{ 
  MyString string; 
  delete[]string.string; 
  if(n>length) 
  { 
   string.length = length; 
   string.string = new char[length+1]; 
   memcpy(string.string,string,length+1); 
    return string; 
  } 
  length = n; 
  string.string = new char[length+1]; 
  memcpy(string.string,string,length+1); 
  return string; 
} 

friend bool operator==(const MyString &str1,const MyString &str2) 
 
  return strcmp(str1.string,str2.string)==0; 
 
friend MyString operator+(const MyString &str1,const MyString &str2) 
{ 
  MyString mystring; 
  char *dest; 
  dest = new char[str1.length+str2.length+1]; 
  memcpy(dest,str1.string,str1.length); 
  memcpy(dest+str1.length,str2.string,str2.length+1); 
  delete[]mystring.string; 
  mystring.string = dest; 
  mystring.length = str1.length+str2.length; 
  return mystring; 
} 
friend ostream &operator<<(ostream &os,const MyString &str) 
{ 
  os<<str.string; 
  return os; 
}