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[1];
        a[0]=0;
        //int len=0;
    }
    else
    {
        len = strlen(cString);//new
        a=new char [len+1];
        strcpy(a,cString);
        //len=strlen(cString);
    }
}

MyString::MyString(const MyString &other){
    int len = strlen(other.a);
    a = new char[len+1];
    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+1];
    strcpy(a, other.a);
    //返回本对象的引用
    return *this;
}

char MyString::at(int index) const
{
    if(len==0)
    {cout<<"no char in string"<<endl;
        return 0;
    }
    if(index>len)
    {
        cout<<"the maximun array exceed"<<endl;
        return 0 ;
    }
    else
    {

        return a[index-1];
    }
}

int MyString::length() const
{
    return len;
}

void MyString::clear()
{
    if(!a)
    {
        delete []a;
        a=NULL;
    }

    len=0;
    //a=" ";
}
bool MyString::empty() const
{
    if(len==0)
        return true;
    else
        return false;
}


int MyString::compare(const MyString& s) const
{
    int m=this->len;int n=s.len;

    for(int i=0;i<m&&i<n;i++)
    {
        if(s.a[i]==a[i])
            continue;
        else if(s.a[i]<a[i])
            return 1;
        else
            return -1;
    }
    return 0;


}
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-1,j=0;i<n+index;i++,j++)
    {
        if(s.a[j]==a[i])
            continue;
        else if(s.a[j]<a[i])
            return 1;
        else
            return -1;
    }
    return 0;
}


void MyString::copy(char s[], int index, int n)
{
    if(n>=len)
    {cout<<"the maximun array exceed"<<endl;}
    else  if(n+index-1>len)
    {
        cout<<"the maximun array exceed"<<endl;
        return;
    }
    else
    {
        for(int i=n-1,j=0;i<n+index-1;i++,j++)
            s[j]=a[i];
    }

}
char* MyString::data() const
{
    return a;
}




int MyString::find(char ch) const
{

    for(int i=0;i<len;i++)
    {
        if(ch==a[i])
            return i+1;
    }

    return 0;
}
int MyString::find(char ch, int index) const
{
    if(index>len||index<1)
    {
        cout<<"the index num is should be  1~ "<<len<<endl;
        return 0;
    }
    for(int i=index-1;i<len;i++)
    {
        if(ch==a[i])
            return i+1;
    }
    return -1;

}

int MyString::find(const MyString& s, int index) const
{
    if(index>s.len||index<1)
    {
        cout<<"the index num is should be  1~ "<<s.len<<endl;
        return 0;
    }
    char ch=s.a[index-1];

    for(int i=0;i<len;i++)
    {
        if(ch==a[i])
            return i+1;
    }

    return 0;
}

// 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 + 1];
    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) == 0)
        return true;
    else
        return false;
}
// >关系运算符重载
bool MyString::operator>(const MyString &other)
{
    if(strcmp(this->a,other.a) > 0)
        return true;
    else
        return false;
}
// <运算符重载
bool MyString::operator<(const MyString &other)
{
    if(strcmp(this->a,other.a) < 0)
        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) + 1;
    char *newstr = new char[len];
    memset(newstr, 0, 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 0;
}