c++ STL string类仿写

最近看string类成员函数的时候，想着自己实现一下类似的字符串类。写了下，大体上粗略的实现了常见的函数，运算符等。有些函数没写重载形式了。主要是封装一个char* 指针，对其作操作.现在想想应该把增大容量的操作封装成一个函数调用，不用每次都实现。。。我是一个小菜鸟，如有错误多多指出。代码如下：

#include <iostream>#include <cstring>using namespace std;class MyString{public:    class Iterator{    public:        Iterator(MyString& ms):_ms(ms),_index(0){}        Iterator(MyString& ms,int index):_ms(ms),_index(index){}        Iterator(const Iterator& it):_ms(it._ms),_index(it._index){}        ~Iterator(){}        char& operator*(){return _ms[_index];}        bool operator==(Iterator it){return _ms==it._ms&&_index==it._index;}        bool operator!=(Iterator it){return !(_ms==it._ms&&_index==it._index);}        Iterator operator++(){++_index;return *this;}        Iterator operator+(int offset){Iterator it(_ms,_index+offset);return it;}        Iterator operator++(int){Iterator it(_ms,_index);++_index;return it;}    private:            int _index;            MyString& _ms;    };public:    MyString();    ~MyString();    MyString(const MyString& ms);    MyString(const char* s);    MyString(int n,char c);    int length(){return _length;}    int size(){return _length;}    void clear();    bool empty(){return _length==0;}    char& back(){return *_data;}    char& front(){return *(_data+_length-1);}    const char* data(){return _data;};    const char* c_str(){return _data;}    int capacity(){return _capacity;}    char& at(int);    char& at(int)const;    MyString& append(const MyString&);    MyString& insert(int index,const MyString&);    MyString& earse(int index,int len);    void swap(MyString&);    MyString substr(int index,int len);    void reverse();    Iterator begin();    Iterator end();    char& operator[](int index);    MyString operator+(MyString&);    void operator+=(MyString&);    void operator+=(const char*);    void operator=(const char*);    void operator=(const MyString&);    friend ostream& operator<<(ostream&,MyString&);    friend istream& operator>>(istream&,MyString&);    friend bool operator==(MyString&,MyString&);    friend void swap(MyString&,MyString&);private:    char *_data;    int _length;    int _capacity;  };MyString::Iterator MyString::begin(){    Iterator it(*this);    return it;}MyString::Iterator MyString::end(){    Iterator it(*this,_length);    return it;}ostream& operator<<(ostream& out,MyString& ms){    out<<ms._data;    return out;}istream& operator>>(istream& in,MyString& ms){    char buffer[1024];    in>>buffer;    ms._length=strlen(buffer);    if(ms._capacity>ms._length){        strcpy(ms._data,buffer);    }    else{        while(ms._capacity<ms._length)ms._capacity*=2;        delete ms._data;        ms._data=new char[ms._capacity];        strcpy(ms._data,buffer);    }    return in;}void swap(MyString& ms1,MyString& ms2){    ms1.swap(ms2);}bool operator==(MyString& ms1,MyString& ms2){    if(strcmp(ms1._data,ms2._data)==0)        return true;    return false;}void MyString::reverse(){    char tmp;    for(int i=0;i<_length/2;i++){        tmp=_data[i];        _data[i]=_data[_length-1-i];        _data[_length-i-1]=tmp;    }}MyString MyString::substr(int index,int len){    if(index<0 || index>=_length)return *this;    if(index+len>_length)len=_length-index;    char *tmp=new char[len+1];    for(int i=index,j=0;i<index+len;i++){        tmp[j++]=_data[i];    }    tmp[len]='\0';    MyString ms(tmp);    delete tmp;    return ms;}void MyString::swap(MyString& ms){    int t=_length;    _length=ms._length;    ms._length=t;    t=_capacity;    _capacity=ms._capacity;    ms._capacity=t;    char *p=_data;    _data=ms._data;    ms._data=p;}MyString& MyString::earse(int index,int len){    if(index<0 || index>=_length)return *this;    if(index+len>_length)len=_length-index;    for(int i=index+len;i<=_length;i++){        _data[i-len]=_data[i];    }    return *this;}MyString& MyString::insert(int index,const MyString&ms){    if(index<0 || index>_length)return *this;    _length=_length+ms._length;    if (_capacity<=_length){        while(_capacity<=_length)_capacity*=2;        char *tmp=new char[_capacity];        strncat(tmp,_data,index);        strcat(tmp,ms._data);        strcat(tmp,_data+index);        delete _data;        _data=tmp;    }    else{        char *tmp=new char[_length-index+1];        strcpy(tmp,_data+index);        strcpy(_data+index,ms._data);        strcat(_data,tmp);        delete tmp;    }    return *this;}MyString& MyString::append(const MyString& ms){    _length=_length+ms._length;    if (_capacity<=_length){        while(_capacity<=_length)_capacity*=2;        char *tmp=new char[_capacity];        strcat(tmp,_data);        strcat(tmp,ms._data);        delete _data;        _data=tmp;    }    else{        strcat(_data,ms._data);    }    return *this;}MyString::MyString():_data(new char('\0')),_length(0),_capacity(1){}MyString::MyString(const char* s):_capacity(1){    _length=strlen(s);    while(_capacity<=_length)_capacity*=2;    _data=new char[_capacity];    strcpy(_data,s);}MyString::MyString(const MyString& ms){    _length=ms._length;    _capacity=ms._capacity;    _data=new char[_capacity];    strcpy(_data,ms._data);}MyString::MyString(int n,char c):_length(n),_capacity(1){    while(_capacity<=_length)_capacity*=2;    _data=new char[_capacity];    char *src=_data;    while(n--){        *src++=c;    }    *src='\0';  }MyString::~MyString(){    if(_data!=NULL){        delete _data;        _data=NULL;    }    _length=0;    _capacity=0;}void MyString::clear(){    *_data='\0';    _length=0;}char& MyString::operator[](int index){    if(index<0 || index>=_length)        return _data[_length];    return _data[index];}MyString MyString::operator+(MyString& ms){    MyString tmp;    while(tmp._capacity<=_length+ms._length)tmp._capacity*=2;    tmp._data=new char[tmp._capacity];    tmp._length=_length+ms._length;    strcat(tmp._data,_data);    strcat(tmp._data,ms._data);    return tmp;}void MyString::operator+=(MyString& ms){    _length=_length+ms._length;    if (_capacity<=_length){        while(_capacity<=_length)_capacity*=2;        char *tmp=new char[_capacity];        strcat(tmp,_data);        strcat(tmp,ms._data);        delete _data;        _data=tmp;    }    else{        strcat(_data,ms._data);    }}void MyString::operator+=(const char* ms){    _length=_length+strlen(ms);    if (_capacity<=_length){        while(_capacity<=_length)_capacity*=2;        char *tmp=new char[_capacity];        strcat(tmp,_data);        strcat(tmp,ms);        delete _data;        _data=tmp;    }    else{        strcat(_data,ms);    }}void MyString::operator=(const char*ms){    _length=strlen(ms);    if(_capacity<=_length){        while(_capacity<=_length)_capacity*=2;        delete _data;        _data=new char[_capacity];    }    strcpy(_data,ms);}void MyString::operator=(const MyString& ms){    _length=strlen(ms._data);    if(_capacity<=_length){        while(_capacity<=_length)_capacity*=2;        delete _data;        _data=new char[_capacity];    }    strcpy(_data,ms._data);}char& MyString::at(int index){    if (index<0 || index>=_length){        return _data[_length];    }    return _data[index];}char& MyString::at(int index)const{    if (index<0 || index>=_length){        return _data[_length];    }    return _data[index];}int main(){    MyString ms="2121";    ms+="abc";    ms.append("789");    cout<<ms<<endl;    ms.insert(0,"ABC");    ms=ms.substr(0,5);    cout<<ms<<endl;    for(MyString::Iterator it=ms.begin();it!=ms.end();++it)        cout<<*it<<' ';    cout<<endl;    cout<<ms.length()<<" "<<ms.size()<<" "<<ms.capacity()<<endl;    return 0;}//结果2121abc789ABC21A B C 2 1 5 5 16