Return a result from a MySQL query in a function after closing connection in C
int CheckBox(char *mac)
{
MYSQL *conn;
MYSQL_RES *res;
MYSQL_ROW row;

/* database details */
char *server = "localhost";
char *user = "user";
char *password = "pw";
char *database = "db";
int retvalue;

conn = mysql_init(NULL);

/* connect to database */
if (!mysql_real_connect(conn, server,user, password, database, 0, NULL, 0))
{
    fprintf(stderr, "%sn", mysql_error(conn));
    exit(1);
}

/* create and send SQL query */
char query[1600];
sprintf(query,"SELECT * FROM boxes WHERE mac = '%s'", mac);
if (mysql_query(conn, query))
{
    fprintf(stderr, "%sn", mysql_error(conn));
    exit(1);
}

res = mysql_use_result(conn);
/* check result to see if we have a hit */
if ((row = mysql_fetch_row(res)) != NULL)
{

    printf("mac (%s) did exist with id %s.n",mac,(char *)row[0]);
    retvalue = (int)row[0];
} else
{
    printf("mac (%s) did NOT exist ",mac);
    /* mac address did not yet exist, so create it */
    sprintf(query,"INSERT INTO boxes (mac) VALUES ('%s')",mac);
    if (mysql_query(conn, query))
    {
        fprintf(stderr, "%sn", mysql_error(conn));
        exit(1);
    } else
    {
        printf("but now doesn");
        CheckBox(mac);
    }
}

/* close connection */
mysql_free_result(res);
mysql_close(conn);

/* return id number of box */
return retvalue;
}