DevOpen

Opens a device and returns the device handle. The device needs to be defined in the CitectSCADA database. If the device cannot be opened, and user error checking is not enabled, the current Cicode task is halted.

You can use this function to return the handle of a device that is already open. The DevOpen() function does not physically open another device - it returns the same device handle as when the device was opened. The mode of the second open call is ignored. To re-open an open device in a different mode, you need to first close the device and then re-open it in the new mode.

When using an ODBC driver to connect to an SQL server or database, experience has shown that connecting only once on startup and not closing the device yields the best performance. ODBC connection is slow and if used on demand may affect your system's performance. Also, some ODBC drivers may leak memory on each connection and may cause errors after a number of re-connects.

Note: If you are opening a database device in indexed mode (nMode=2), an index file will automatically be created by CitectSCADA if one does not already exist. If you feel a device index has become corrupt, delete the existing index file and a new one will be created the next time the DevOpen function is run.

0 - Open the device in shared mode - the default mode when opening a device if none is specified.

1 - Open the device in exclusive mode. In this mode only one user can have the device open. The open will return an error if another user has the device open in shared or exclusive mode.

2 - Open the device in indexed mode. In this mode the device will be accessed in index order. This mode is only valid if the device is a database device and has an index configured in the Header field at the Devices form. Please be aware that specifying mode 2 when opening an ASCII device is ignored internally.

4 - Open the device in 'SQL not select' mode. If opened in this mode, you need to not attempt to read from an SQL device.

8 - Open the device in logging mode. In this mode the history files will be created automatically.

16 - Open the device in read only mode. In this mode data can be viewed, but not written. This mode is supported only by DBF and ASCII files - it is ignored by printers and SQL/ODBC databases.

The device handle. If the device cannot be opened, -1 is returned. The device handle identifies the table where all data on the associated device is stored.

INT

FUNCTION

PrintRecipe(STRING sCategory)

	STRING sRecipe;

	INT hRecipe, hPrinter;

	ErrSet(1); ! enable user error checking

	hRecipe = DevOpen("Recipe", 0);

	IF hRecipe = -1 THEN

		DspError("Cannot open recipe");

		RETURN FALSE;

	END

	hPrinter = DevOpen("Printer1", 0);

	IF hPrinter = -1 THEN

		DspError("Cannot open printer");

		RETURN FALSE;

	END

	ErrSet(0); ! disable user error checking

	WHILE NOT DevEof(hRecipe) DO

		sRecipe = DevReadLn(hRecipe);

		DevWriteLn(hPrinter, sRecipe);

	END

	DevClose(hRecipe);

	DevClose(hPrinter);

	RETURN TRUE;

END