Handling Errors

We're nearly ready to put our program together! There's just one more important thing to include: error handling.

Nearly all the API's functions return a value indicating success or failure. If a function fails, you can use mysql_error() and mysql_errno() to report on what went wrong.

For example, we will test the result of mysql_real_connect(). As you saw just now, it returns a MYSQL* connection handle if the connection attempt succeeds, or NULL if it fails. Let's add some error handling to our connection routine, which should now look like this:

if (mysql_real_connect (
    mysql,
    db_host,
    db_user,
    db_pass,
    db_name,
    db_port,
    unix_socket,
    db_flags) == NULL ) {
    fprintf (stderr,
        "mysql_real_connect() failed!
Error %u: %s
",
        mysql_errno (mysql),
        mysql_error (mysql));
    return (NULL);
}

The functions mysql_error() and mysql_errno() return the error message and error code, respectively, for the most recent API call that could succeed or fail. They take the MYSQL* database connection handle as their argument.

The preceding code example tests the result of mysql_real_connect() and prints an error message if the connection fails together with some error information. For example, a failed connection attempt might generate the following output:

Error 1045: Access denied for user: 'tonyb@localhost' (Using password: YES)