Superkkt Blog

/*
 * SQLite3 Online Backup Tool
 *
 * Kitae Kim <superkkt@sds.co.kr>
 *
 * <Compile Instruction>
 *  $ sudo apt-get install libsqlite3-dev
 *  $ g++ -Wall -O2 -o sqlite_online_backup sqlite_online_backup.cpp -lsqlite3
 */
#include <iostream>
#include <cstdlib>
#include <cstdio>

#include <sqlite3.h>

/*
** This function is used to load the contents of a database file on disk
** into the "main" database of open database connection pInMemory, or
** to save the current contents of the database opened by pInMemory into
** a database file on disk. pInMemory is probably an in-memory database,
** but this function will also work fine if it is not.
**
** Parameter zFilename points to a nul-terminated string containing the
** name of the database file on disk to load from or save to. If parameter
** isSave is non-zero, then the contents of the file zFilename are
** overwritten with the contents of the database opened by pInMemory. If
** parameter isSave is zero, then the contents of the database opened by
** pInMemory are replaced by data loaded from the file zFilename.
**
** If the operation is successful, SQLITE_OK is returned. Otherwise, if
** an error occurs, an SQLite error code is returned.
*/
int loadOrSaveDb(sqlite3 *pInMemory, const char *zFilename, int isSave){
  int rc;                   /* Function return code */
  sqlite3 *pFile;           /* Database connection opened on zFilename */
  sqlite3_backup *pBackup;  /* Backup object used to copy data */
  sqlite3 *pTo;             /* Database to copy to (pFile or pInMemory) */
  sqlite3 *pFrom;           /* Database to copy from (pFile or pInMemory) */

  /* Open the database file identified by zFilename. Exit early if this fails
  ** for any reason. */
  rc = sqlite3_open(zFilename, &pFile);
  if( rc==SQLITE_OK ){

    /* If this is a 'load' operation (isSave==0), then data is copied
    ** from the database file just opened to database pInMemory.
    ** Otherwise, if this is a 'save' operation (isSave==1), then data
    ** is copied from pInMemory to pFile.  Set the variables pFrom and
    ** pTo accordingly. */
    pFrom = (isSave ? pInMemory : pFile);
    pTo   = (isSave ? pFile     : pInMemory);

    /* Set up the backup procedure to copy from the "main" database of
    ** connection pFile to the main database of connection pInMemory.
    ** If something goes wrong, pBackup will be set to NULL and an error
    ** code and  message left in connection pTo.
    **
    ** If the backup object is successfully created, call backup_step()
    ** to copy data from pFile to pInMemory. Then call backup_finish()
    ** to release resources associated with the pBackup object.  If an
    ** error occurred, then  an error code and message will be left in
    ** connection pTo. If no error occurred, then the error code belonging
    ** to pTo is set to SQLITE_OK.
    */
    pBackup = sqlite3_backup_init(pTo, "main", pFrom, "main");
    if( pBackup ){
      (void)sqlite3_backup_step(pBackup, -1);
      (void)sqlite3_backup_finish(pBackup);
    }
    rc = sqlite3_errcode(pTo);
  }

  /* Close the database connection opened on database file zFilename
  ** and return the result of this function. */
  (void)sqlite3_close(pFile);
  return rc;
}

int main(int argc, char **argv)
{
    if (argc != 3) {
        std::cerr << "Usage: " << argv[0] << " db_file backup_file\n";
        exit(EXIT_FAILURE);
    }

    sqlite3 *db = NULL;
    if (sqlite3_open(argv[1], &db) != SQLITE_OK) {
        std::cerr << "Failed to open the database file..\n";
        exit(EXIT_FAILURE);
    }

    int rc = loadOrSaveDb(db, argv[2], 1);
    if (rc != SQLITE_OK) {
        (void) sqlite3_close(db);
        std::cerr << "Failed to backup the database file.. (errno: " << rc << ")\n";
        exit(EXIT_FAILURE);
    }

    (void) sqlite3_close(db);

    return 0;
}