[완료] C를 OOP처럼 구성하고자 하였을 때 this 키워드의 구현방법

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
typedef struct string{
    //Class variable
    char *data;
    int length;
 
    //Class methods
    int (*get_length)(struct string *this);
    void (*add_string)(struct string *this, char *str);
    void (*change_string)(struct string *this, char *str);
    void (*show_string_info)(struct string *this);
}string;
 
int get_length(string *this)
{
    return this->length;
}
 
void add_string(string *this, char *str)
{
   strcat(this->data,str);
   this->length = strlen(this->data);
}
 
void change_string(string *this, char *str)
{
    if (NULL != this->data);
	free(this->data);
 
    this->data = strdup(str);
    this->length = strlen(this->data);
 
}
 
void show_string_info(string *this)
{
    printf("String : %s\n",this->data);
    printf("Length : %d\n",this->length);
}
 
string *create_string(char *data)
{
    string *s;
    s = (string *)malloc(sizeof(string));
    s->get_length = get_length;
    s->add_string = add_string;
    s->change_string = change_string;
    s->show_string_info = show_string_info;
 
    s->data = strdup(data);
    s->length = strlen(s->data);
 
    return s;
}
 
void delete_string(string *this)
{
    if (NULL != this->data)
	free(this->data);
    if (NULL != this)
	free(this);
}
 
 
int main()
{
 
    string *first = NULL, *second = NULL;
 
    first = create_string("abcdefg");
    second = create_string("EEE");
 
    first->show_string_info(first);
 
    first->change_string(first, "12345678");
    first->show_string_info(first);
 
    first->add_string(first,second->data);
    first->show_string_info(first);
 
    first->change_string(first,"abc");
    first->show_string_info(first);
 
    delete_string(first);
    delete_string(second);
}