C++面试重难点 ：自实现string类

一、myString

class myString
{
public:
    myString(const char * str=nullptr);
    ~myString();
    myString(const myString & another);
    //*****************运算符重载*****************//
    myString & operator= (const myString & another);
    bool operator== (const myString & another);
    bool operator> (const myString & another);
    bool operator< (const myString & another);
    myString operator+ (const myString & another);
    myString & operator+= (const myString & another);
    char operator[] (int i);
    //********************************************//
    char at(int i);
    char * c_str();
private:
    char * str_;
};

二、实现

（1）构造器（构造函数）

myString(const char * str=nullptr)
{
  if(nullptr==str)//空字符串
  {
     str_=new char[1];
     *str_='\0';
  }
  else
  {
    str_=new char[strlen(str)+1];//非空字符串
    strcpy(str_,str);
  }
}

（2）析构器（析构函数）

~myString()
{
    delete []str_;
}

（3）拷贝构造

myString(const myString & another)
{
    str_=new char[strlen(another.str_)+1];
    strcpy(str_,another.str_);
}

（4）运算符重载

myString & operator= (const myString & another)
{
    if(this==&another)
        return *this;
    delete []this->str_;
    str_=new char[strlen(another.str_)+1];
    strcpy(str_,another.str_);
    return *this;
}
bool operator== (const myString & another)
{
    return strcmp(this->str_,another.str_)==0;
}
bool operator> (const myString & another)
{
    return strcmp(this->str_,another.str_)>0;
}

bool operator< (const myString & another)
{
    return strcmp(this->str_,another.str_)<0;
}
myString operator+ (const myString & another)
{
    myString ms;
    delete []ms.str_;
    ms.str_=new char[strlen(this->str_)+strlen(another.str_)+1]{0};
    strcat(strcat(ms.str_,this->str_),another.str_);
    return ms;
}
myString & operator+= (const myString & another)
{
    int catLen=strlen(this->str_);
    int srcLen=strlen(another.str_);
    this->str_=static_cast<char*>(realloc(this->str_,catLen+srcLen+1));
    memset(this->str_+catLen,0,srcLen+1);
    strcat(this->str_,another.str_);
    return *this;
}
char operator[] (int i)
{
    return str_[i];
}

（5）其它

char at(int i)
{
    return str_[i];
}
char * c_str()
{
    return str_;
}

三、测试

#include <iostream>
#include<string.h>
using namespace std;

class myString
{
public:
    myString(const char * str=nullptr)//构造
    {
      if(nullptr==str)
      {
         str_=new char[1];
         *str_='\0';
      }
      else
      {
        str_=new char[strlen(str)+1];
        strcpy(str_,str);
      }
    }
    ~myString()//析构
    {
        delete []str_;
    }
    myString(const myString & another)//拷贝构造
    {
        str_=new char[strlen(another.str_)+1];
        strcpy(str_,another.str_);
    }

    //*****************运算符重载*****************//
    myString & operator= (const myString & another)
    {
        if(this==&another)
            return *this;
        delete []this->str_;
        str_=new char[strlen(another.str_)+1];
        strcpy(str_,another.str_);
        return *this;
    }
    bool operator== (const myString & another)
    {
        return strcmp(this->str_,another.str_)==0;
    }
    bool operator> (const myString & another)
    {
        return strcmp(this->str_,another.str_)>0;
    }

    bool operator< (const myString & another)
    {
        return strcmp(this->str_,another.str_)<0;
    }
    myString operator+ (const myString & another)
    {
        myString ms;
        delete []ms.str_;
        ms.str_=new char[strlen(this->str_)+strlen(another.str_)+1]{0};
        strcat(strcat(ms.str_,this->str_),another.str_);
        return ms;
    }
    myString & operator+= (const myString & another)
    {
        int catLen=strlen(this->str_);
        int srcLen=strlen(another.str_);
        this->str_=static_cast<char*>(realloc(this->str_,catLen+srcLen+1));
        memset(this->str_+catLen,0,srcLen+1);
        strcat(this->str_,another.str_);
        return *this;
    }
    char operator[] (int i)
    {
        return str_[i];
    }
    //********************************************//


    char at(int i)
    {
        return str_[i];
    }
    char * c_str()
    {
        return str_;
    }
    void dis()
    {
        cout<<"myString:"<<str_<<endl;
    }
private:
    char * str_;
};

int main()
{
    string s;
    myString ms;
    cout <<"string: "<< s<<"         ";
    ms.dis();

    string s1("china");
    myString ms1("china");
    cout <<"string: "<< s1<<"    ";
    ms1.dis();

    string s2(s1);
    myString ms2(ms1);
    cout <<"string: "<< s2<<"    ";
    ms2.dis();

    string s3;
    s3=s2;
    myString ms3;
    ms3=ms2;
    cout <<"string: "<< s3<<"    ";
    ms3.dis();

    string s4("china");
    if(s1<s4)
        cout<<"<"<<endl;
    else if(s1>s4)
        cout<<">"<<endl;
    else
        cout<<"=="<<endl;

    myString ms4("china");
    if(ms1<ms4)
        cout<<"<"<<endl;
    else if(ms1>ms4)
        cout<<">"<<endl;
    else
        cout<<"=="<<endl;

    string s5=" is powerful!";
    string s6=s3+s5;
    cout <<"string: "<< s6<<"            "
                            "  ";

    myString ms5=" is powerful!";
    myString ms6=ms3+ms5;
    ms6.dis();

    string s7("beautiful!");
    s6+=s7;
    cout <<"string: "<< s6<<"    ";

    myString ms7("beautiful!");
    ms6+=ms7;
    ms6.dis();

    cout <<"string: "<< s6[3]<<"   ";
    cout <<"myString:"<<ms6[3]<<endl;

    cout <<"string: "<< s6.at(9)<<"   ";
    cout <<"myString:"<<ms6.at(9)<<endl;

    cout <<"string: "<< s6.c_str()<<"    ";
    cout <<"myString:"<<ms6.c_str()<<endl;

    return 0;
}