【重温】C++中String类的实现

#include<iostream>

using namespace std;

class String{

     friend ostream& operator<< (ostream&,String&);

public:

     String(const char* str=NULL);                 //赋值构造兼默认构造函数(char)

     String(const String &other);                  //赋值构造函数(String)

     String& operator=(const String&other);        //operator=

     String operator+(const String &other)const;   //operator+

     bool operator==(const String&);               //operator==

     char& operator[](unsigned int);               //operator[]

     size_t size(){return strlen(m_data);};

     ~String(void) {delete[] m_data;}

private:

     char *m_data;

};

inline String::String(const char* str)

{

     if (!str) m_data=0;

     else

     {

         m_data = new char[strlen(str)+1];

         strcpy(m_data,str);

     }

}

inline String::String(const String& other)

{

     if(!other.m_data) m_data=0;

     else

     {

         m_data=new char[strlen(other.m_data)+1];

         strcpy(m_data,other.m_data);

     }

}

inline String& String::operator=(const String& other)

{

     if (this!=&other)

     {

         delete[] m_data;

         if(!other.m_data) m_data=0;

         else

         {

             m_data = new char[strlen(other.m_data)+1];

             strcpy(m_data,other.m_data);

         }

     }

     return *this;

}

inline String String::operator+(const String &other)const

{

     String newString;

     if(!other.m_data)

         newString = *this;

     else if(!m_data)

         newString = other;

     else

     {

         newString.m_data = new char[strlen(m_data)+strlen(other.m_data)+1];

         strcpy(newString.m_data,m_data);

         strcat(newString.m_data,other.m_data);

     }

     return newString;

}

inline bool String::operator==(const String &s)     

{

     if ( strlen(s.m_data) != strlen(m_data) )

         return false;

     return strcmp(m_data,s.m_data)?false:true;

}

inline char& String::operator[](unsigned int e)

{

     if (e>=0&&e<=strlen(m_data))

         return m_data[e];

}

ostream& operator<<(ostream& os,String& str)

{

     os << str.m_data;

     return os;

}

void main()

{

     String str1="Hello!";

     String str2="Teacher!";

     String str3 = str1+str2;

     cout<<str3<<"\n"<<str3.size()<<endl;

}