learning c :D

gistfile1.c

#include <stdio.h>
#include <stdlib.h>

struct db_element {
    int    id;
    char*  key;
    char*  value;
    void*  next;
    struct db_element_collection* db;
};
typedef struct db_element DB_ELEMENT;

struct db_element_collection {
    int                size;
    struct db_element* first;
    struct db_element* last;
};
typedef struct db_element_collection DB;

// init new DB
DB* DB_init(void) {
  DB* db = malloc(sizeof(DB));
  db -> size = 0;

  return db;
};

// create new DB_ELEMENT in DB
DB_ELEMENT* DB_create_element(DB* _db, char* _key, char* _value) {
    // allocate new object
    DB_ELEMENT* element = malloc(sizeof(DB_ELEMENT));
    
    // set db
    element -> db = _db;

    // set values
    element -> key = _key;
    element -> value = _value;


    // assign first element in DB if needed
    if (element -> db -> size == 0) { 
      element -> db -> first = element; 
    } else {
      element -> db -> last -> next = (void*) element;
    }

    // assign last
    element -> db -> last = element;

    // increase DB size
    element -> db -> size = (element -> db -> size + 1);

    // assign id
    element -> id = element -> db -> size;

    return element;
};

// get next element
DB_ELEMENT* DB_get_next(DB_ELEMENT* element) {
    return (DB_ELEMENT*)(element -> next);
};

// find element in db by key
DB_ELEMENT* DB_find_by_key(DB* _db, char* _search_key) {
    DB_ELEMENT* current = NULL;
    DB_ELEMENT* result  = NULL;

    if (_db -> first) {
      current = _db -> first;
    }

    while (current) {
      if (current -> key == _search_key) {
        result = current;
        break;
      } else {
        DB_ELEMENT* _next = DB_get_next(current);

        if (_next) {
            current = _next;
        } else {
            break; 
        }
      }
    }

    return result;
}

void DB_DEBUG_find_by_key(DB* _db, char* _search_key) {
    DB_ELEMENT* result = DB_find_by_key(_db, _search_key);

    if (result != NULL) {
        printf("search result for key [%s] -> %s\n", _search_key, result -> value);
    } else {
        printf("result not found for key [%s]\n", _search_key);
    }
}

// seed data
void DB_create_test_data(DB* _db) {
    DB_create_element(_db, "andrey", "3112142");
    DB_create_element(_db, "anton", "2343434");
    DB_create_element(_db, "stepa", "304394943");
    DB_create_element(_db, "sergey", "494949499");
    DB_create_element(_db, "vera", "393939");
}

int main(void) {
    DB* db = DB_init();
    DB_create_test_data(db);

    DB_DEBUG_find_by_key(db, "anton");
    DB_DEBUG_find_by_key(db, "kilogramm");
};