MyString(重写String)

http://wenku.baidu.com/view/d7ac113243323968011c925b.html

已知类String的原型为：

class String{
public:
    String(const char *str = NULL); // 普通构造函数
    String(const String &other);     // 拷贝构造函数
    ~ String(void);         // 析构函数
    String & operator =(const String &other);// 赋值函数
private:
    char   *m_data;    // 用于保存字符串
};

请编写String的上述4个函数。

 /*
 ccnu_hupo_cpp_class_tst6exercise2_by:lele_2013_10_30
    new不忘delete
 Design the string class in the C++ library by providing your own implementation for the following functions (name your class MyString):
 
 MyString();//构造
 MyString(const char* cString);//地址不能变
 char at(int index) const;//输入数组下标，返回字符
 int length() const;//长度
 void clear();//清空 len=0
 bool empty() const;//是否清空？len不变
 int compare(const MyString& s) const;//
 int compare(int index, int n, const MyString& s) const;
 void copy(char s[], int index, int n);
 char* data() const;
 int find(char ch) const;
 int find(char ch, int index) const;
 int find(const MyString& s, int index) const;
 
 */
 
 #include<iostream>
 #include<string.h>
 using namespace std;
 class MyString
 {
 public:
     MyString(void):a(NULL){cout << "MyString()" << endl;}
     MyString(const char* cString=NULL);//ordinary func
     MyString(const MyString &other);//copy func
     MyString & operator =(const MyString &other);//assign func
     //~MyString(void);
     char at(int index) const;//
     int length() const;
     void clear();
     bool empty() const;
     int compare(const MyString& s) const;
     int compare(int index, int n, const MyString& s) const;
     void copy(char s[], int index, int n);
     char* data() const;
     int find(char ch) const;
     int find(char ch, int index) const;
     int find(const MyString& s, int index) const;
 
     // MyString &operator+=(const MyString &other);
     //MyString operator +(const MyString &mystr);
     //MyString &operator +(const MyString &mystr);
     //重载为友元函数,重载"+"运算符(不改变被加对象)  注意返回引用不行
     friend MyString operator +(const MyString& mystr1,const MyString &mystr2);
     MyString &operator+=(const MyString &other);
 
     bool operator > (const MyString & another);
     bool operator < (const MyString & another);
     bool operator == (const MyString & another);
 
     char& operator[](int idx);
 
     void dis();
     friend ostream& operator<<(ostream& os,const MyString& other);
 
     ~MyString();
 
 private:
     char *a;
     int len;
 };
 
 //MyString::MyString(){
 //    cout << "MyString()" << endl;
 //}
 MyString::~MyString(){
     cout<<"~MyString():delete..."<<endl;
     delete []a;
 }
 
 MyString::MyString(const char* cString)
 {
     if (cString==NULL)
     {
         a=new char[];
         a[]=;
         //int len=0;
     }
     else
     {
         len = strlen(cString);//new
         a=new char [len+];
         strcpy(a,cString);
         //len=strlen(cString);
     }
 }
 
 MyString::MyString(const MyString &other){
     int len = strlen(other.a);
     a = new char[len+];
     strcpy(a, other.a);
 }
 
 MyString &MyString::operator =(const MyString &other){
     //self check assign
     if(this == &other){
         return *this;
     }
     //释放原有的内存资源
     delete []a;
     //分配新的内存资源，并复制内容
     int len = strlen(other.a);
     a = new char[len+];
     strcpy(a, other.a);
     //返回本对象的引用
     return *this;
 }
 
 char MyString::at(int index) const
 {
     if(len==)
     {cout<<"no char in string"<<endl;
         return ;
     }
     if(index>len)
     {
         cout<<"the maximun array exceed"<<endl;
         return  ;
     }
     else
     {
 
         return a[index-];
     }
 }
 
 int MyString::length() const
 {
     return len;
 }
 
 void MyString::clear()
 {
     if(!a)
     {
         delete []a;
         a=NULL;
     }
 
     len=;
     //a=" ";
 }
 bool MyString::empty() const
 {
     if(len==)
         return true;
     else
         return false;
 }
 
 int MyString::compare(const MyString& s) const
 {
     int m=this->len;int n=s.len;
 
     for(int i=;i<m&&i<n;i++)
     {
         if(s.a[i]==a[i])
             continue;
         else if(s.a[i]<a[i])
             return ;
         else
             return -;
     }
     return ;
 
 }
 int MyString::compare(int index, int n, const MyString& s) const
 {
     int m=len,k=s.len;
     if(index+n>m||index+n>k)
     {
         cout<<"cannot compare!"<<endl;
         ///I dont know how to solve it
     }
     for(int i=index-,j=;i<n+index;i++,j++)
     {
         if(s.a[j]==a[i])
             continue;
         else if(s.a[j]<a[i])
             return ;
         else
             return -;
     }
     return ;
 }
 
 void MyString::copy(char s[], int index, int n)
 {
     if(n>=len)
     {cout<<"the maximun array exceed"<<endl;}
     else  if(n+index->len)
     {
         cout<<"the maximun array exceed"<<endl;
         return;
     }
     else
     {
         for(int i=n-,j=;i<n+index-;i++,j++)
             s[j]=a[i];
     }
 
 }
 char* MyString::data() const
 {
     return a;
 }
 
 int MyString::find(char ch) const
 {
 
     for(int i=;i<len;i++)
     {
         if(ch==a[i])
             return i+;
     }
 
     return ;
 }
 int MyString::find(char ch, int index) const
 {
     if(index>len||index<)
     {
         cout<<"the index num is should be  1~ "<<len<<endl;
         return ;
     }
     for(int i=index-;i<len;i++)
     {
         if(ch==a[i])
             return i+;
     }
     return -;
 
 }
 
 int MyString::find(const MyString& s, int index) const
 {
     if(index>s.len||index<)
     {
         cout<<"the index num is should be  1~ "<<s.len<<endl;
         return ;
     }
     char ch=s.a[index-];
 
     for(int i=;i<len;i++)
     {
         if(ch==a[i])
             return i+;
     }
 
     return ;
 }
 
 // 加法运算符重载
 //MyString MyString::operator +(const MyString & another){
 //    int len = strlen(this->a) + strlen(another.a);
 //    MyString str("");
 
 //    delete []str.a;
 //    str.a = new char[len + 1];
 //    memset(str.a,0,len + 1);
 //    //int len1 = strlen(this->a) + 1;
 //    //strcat_s(str.a, len1, this->a);
 //    strcat(str.a, this->a);
 //    // 源串长度 + 目标串长度 + 结束符
 //    //int len2 = strlen(this->a) + strlen(another.a) + 1;
 //    //strcat_s(str.a,len2, another.a);
 //    strcat(str.a, another.a);
 //    return str;
 //}
 
 //MyString MyString::operator +(const MyString &mystr){//mem leak
 //    MyString newString("");
 //    if (!mystr.a)
 //     newString = *this;
 //    else if (!a)
 //     newString = mystr;
 //    else {
 //     newString.a = new char[strlen(a) + strlen(mystr.a) + 1];
 //     strcpy(newString.a, a);
 //     strcat(newString.a, mystr.a);
 //    }
 //    return newString;
 //}
 
 //重载"+"运算符(不改变被加对象)
 //MyString &MyString::operator +(const MyString &mystr){
 //    MyString *temp=new MyString("");
 //    temp->a=new char[strlen(a)+strlen(mystr.a)+1];
 //    strcpy(temp->a,a);
 //    strcat(temp->a,mystr.a);
 //    return *temp;
 //}
 
 /*
     //重载"+"运算符(改变被加对象)
     Mystring &operator +(Mystring &mystr){
         char *temp=str;
         str=new char[strlen(temp)+strlen(mystr.str)+1];
         strcpy(str,temp);
         strcat(str,mystr.str);
         delete [] temp;
         return *this;
     }
     */
 //friend
 MyString operator +(const MyString& mystr1,const MyString &mystr2){
     MyString str("");
     delete[] str.a;
     str.len =  strlen(mystr1.a)+strlen(mystr2.a);
     str.a = new char[str.len + ];
     strcpy(str.a, mystr1.a);
     strcat(str.a, mystr2.a);
     return str;
 
     //    //MyString *temp=new MyString("");//mem leak
     //    MyString temp("");
     //    temp.a=new char[strlen(mystr1.a)+strlen(mystr2.a)+1];
     //    //temp->a=new char[strlen(mystr1.a)+strlen(mystr2.a)+1];
     //    strcpy(temp.a,mystr1.a);
     //    strcat(temp.a,mystr2.a);
     //    return temp;
 }
 
 // ==关系运算符重载
 bool MyString::operator==(const MyString &other)
 {
     if(strcmp(this->a,other.a) == )
         return true;
     else
         return false;
 }
 // >关系运算符重载
 bool MyString::operator>(const MyString &other)
 {
     if(strcmp(this->a,other.a) > )
         return true;
     else
         return false;
 }
 // <运算符重载
 bool MyString::operator<(const MyString &other)
 {
     if(strcmp(this->a,other.a) < )
         return true;
     else
         return false;
 }
 // []运算符重载
 char& MyString::operator[](int idx)
 {
     return a[idx];
 }
 
 ostream& operator<<(ostream& os,const MyString& other){
     return os << other.a;
 }
 
 MyString &MyString::operator+=(const MyString &other)
 {
     int len = strlen(a) + strlen(other.a) + ;
     char *newstr = new char[len];
     memset(newstr, , len);
     strcpy(newstr, a);
     strcat(newstr, other.a);
 
     delete[] a;
 
     a = newstr;
     return *this;
 }
 
 int main(){
     MyString ms="hello";
 
     MyString mt("world");
     mt += ms;
     cout << mt << endl;
     return ;
 }