C++ 自己实现一个string类

#include <iostream>
#include <string.h>

using namespace std;

#define KSTRING_BUFF_MAX        100

#define KSTRING_DEFAULT_CH      

class kstring
{
private:
    char data[KSTRING_BUFF_MAX];
    int  data_p;

public:
    kstring(void)
    {
        memset(this->data, KSTRING_DEFAULT_CH, sizeof(this->data));
        this->data_p = 0;
    }

    kstring(kstring &str)
    {
        *this = str;
    }

    kstring(const char *str)
    {
        *this = str;
    }

    kstring(int size = 0, char ch = KSTRING_DEFAULT_CH)
    {
        memset(this->data, KSTRING_DEFAULT_CH, sizeof(this->data));
        memset(this->data, ch, size);
        this->data_p = size;
    }

    ~kstring(void)
    {
        cout << "~kstring" << endl;
        memset(this->data, KSTRING_DEFAULT_CH, sizeof(this->data));
        this->data_p = 0;
    }

    bool empty(void)
    {
        if(this->data_p > 0)
            return true;
        else
            return false;
    }

    int size(void)
    {
        return this->data_p;
    }

    void testout(void)
    {
        cout << this->data_p << ":" << this->data << endl;
    }

    char& operator [](int i)
    {
        return this->data[i];
    }

    kstring& operator =(kstring &str)
    {
        memset(this->data, KSTRING_DEFAULT_CH, sizeof(this->data));
        this->data_p = str.size();
        strcpy(this->data, &str[0]);

        return *this;
    }
    
    kstring& operator =(const char *str)
    {
        memset(this->data, KSTRING_DEFAULT_CH, sizeof(this->data));
        this->data_p = strlen(str);
        strcpy(this->data, str);
        
        return *this;
    }

    kstring operator +(kstring &str)
    {
        kstring temp(this->size() + str.size());
        
        strcpy(&temp[0], this->data);
        strcpy(&temp[this->data_p], &str[0]);

        return temp;
    }

    kstring operator +(const char *str)
    {
        kstring temp(this->size() + strlen(str));
        
        strcpy(&temp[0], this->data);
        strcpy(&temp[this->data_p], str);

        return temp;
    }

    kstring& operator +=(kstring &str)
    {
        strcpy(&this->data[this->data_p], &str[0]);
        this->data_p += str.size();

        return *this;
    }

    kstring& operator +=(const char *str)
    {
        strcpy(&this->data[this->data_p], str);
        this->data_p += strlen(str);

        return *this;
    }

    bool operator ==(kstring &str)
    {
        if(this->size() != str.size())
            return false;

        if(strcmp(this->data, &str[0]) == 0)
            return true;

        return false;
    }

    friend ostream& operator <<(ostream &output, const kstring &str)
    {
        output << str.data;
        return output;
    }

    friend istream& operator >>(istream &input, kstring &str)
    {
        input >> str.data;
        str.data_p = strlen(str.data);
        return input;
    }
};