#ifndef GH_DATASTORE_H
#define GH_DATASTORE_H

#include <sqlite3.h>

struct reading
{
  int   id;
  char *title;
  int   readmill_id;
  int   total_pages;
};

sqlite3 *gh_datastore_open_db (char *data_dir);

int gh_datastore_get_db_version (sqlite3 *db);
void gh_datastore_set_db_version (sqlite3 *db, int version);

#endif

#ifndef GH_DATASTORE_H
#define GH_DATASTORE_H

#include <sqlite3.h>

typedef struct
{
  int   id;
  char *title;
  int   readmill_id;
  int   total_pages;
} Reading;

sqlite3 *gh_datastore_open_db (char *data_dir);

int gh_datastore_get_db_version (sqlite3 *db);
void gh_datastore_set_db_version (sqlite3 *db, int version);

#endif

Use typedef for reading struct
Use typedef for reading struct