Re: [Boost-users] [boost::system] Is the library abstraction general enough?

On Mon, Feb 23, 2009 at 2:33 AM, Lian Cheng wrote:

Boris Schaeling:

...

On Fri, 20 Feb 2009 09:36:53 +0100, Lian Cheng wrote:

Isn't there a list of error numbers and error strings MySQL uses? I ask as calling error_category::message() should also return an error string even if no MySQL connection is used?

Unfortunately, no. As I've mentioned, the error strings MySQL uses are printf format strings, such as:

Using unsupported buffer type: %d (parameter: %d)

And you always need an active MySQL connection handle to obtain the full error message by calling mysql_error(). And you can never get the message back once you close the connection:

MYSQL* conn = mysql_init( 0 ); // do something causes an error. mysql_close( conn ); printf( "error: %s", mysql_error( conn ) ); // Messed up.

Boost Exception can be used to transport anything in an exception object. You can transport error codes as well as error messages: #include typedef boost::error_info mysql_error_code; typedef boost::error_info mysql_error_string; struct mysql_err: std::exception, boost::exception { }; .... if( int error=mysql_query(conn,....) ) throw mysql_err() << mysql_error_code(error) << mysql_error_string(mysql_error(conn)); Alternatively, if you use shared_ptr to manage the lifetime of the MYSQL connection, as in: boost::shared_ptr<MYSQL> conn( mysql_init(0), mysql_close ); you can use an exception object to keep the connection afloat: typedef boost::error_info mysql_error_code; typedef boost::error_info mysql_conn; struct mysql_err: std::exception, boost::exception { }; .... if( int error=mysql_query(conn,....) ) throw mysql_err() << mysql_error_code(error) << mysql_conn(conn); Now, when you catch mysql_err, you can talk to mysql to get the error message: catch( mysql_err & x ) { boost::shared_ptr<MYSQL> conn=*boost::get_error_info(x); char const * msg=mysql_error(conn.get()); .... } Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode