重温String类实现

面试时经常会被问到的，请自己实现以下String类。考的很基础的知识，还有考虑问题是否全面。

class String{

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

public:

    String(const char* str=NULL);                //...........(char)

    String(const String &other);                 //......(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;

}