#pragma once

class string

{

public:

    string(const char* str = nullptr);

    string(const string& str);

    ~string();

    string& operator=(const string& str);

    string& operator+=(const string& str);

    char& operator[](int n) const;

    char& operator[](int n);

    bool operator==(const string& str) const;

    int size() const;

    const char* c_str() const;

    bool empty() const;

    friend const string operator+(const string& lhs, const string& rhs);

private:

    char *data;

    int length;

};

#include "string.h"

#include <string.h>

#include <stdio.h>

const string operator+(const string& lhs, const string& rhs)

{

    string tmp(lhs);

    tmp += rhs;

    return tmp;

}

string::string(const char * str)

{

    if (!str)

    {

        length = ;

        data = new char[];

        *data = '\0';

    }

    else

    {

        length = strlen(str);

        data = new char[length + ];

        strcpy(data, str);

    }

    printf("string constructor\n");

}

string::string(const string & str)

{

    length = str.size();

    data = new char[length + ];

    strcpy(data, str.c_str());

    printf("string copy constructor\n");

}

string::~string()

{

    length = ;

    delete[] data;

    printf("string destructor\n");

}

string& string::operator=(const string & str)

{

    if (this == &str)

        return *this;

    delete[] data;

    length = str.size();

    data = new char[length + ];

    strcpy(data, str.c_str());

    return *this;

}

string & string::operator+=(const string & str)

{

    length += str.size();

    char *newdata = new char[length + ];

    strcpy(newdata, data);

    strcat(newdata, str.c_str());

    delete[] data;

    data = newdata;

    return *this;

}

char& string::operator[](int n) const

{

    return data[n];

}

char& string::operator[](int n)

{

    return data[n];

}

bool string::operator==(const string & str) const

{

    if (length != str.size())

        return false;

    return strcmp(data, str.c_str()) ? false : true;

}

int string::size() const

{

    return length;

}

const char * string::c_str() const

{

    return data;

}

bool string::empty() const

{

    return length == ;

}

#include"string.h"

int main()

{

    char a[] = "hello", b[] = "world";

    string s1(a), s2(b);

    string s3 = s1 + s2;

    return ;

}

string constructor

string constructor

string copy constructor

string destructor

string destructor

string destructor