As I understand it, the NULL device is a kludge to hide unwanted output from API's in VistA that are supposed to be I/O free but are not. The "silent" Fileman DBS API's, for instance, supposedly communicate with their calling applications entirely by setting values in arrays designated by their input parameters (see http://www.hardhats.org/fileman/pm/db_intro.htm), but they sometimes produce I/O on their current device intended for the old dumb terminal interface.
I encountered this while experimenting with the API's for field validation, such as CHK^DIE, with web applications. This means that servers such as the CPRS broker and M2Web must USE a NULL device or other alternate device before calling any VistA API's or risk having their server-to-client communications broken by unwanted I/O. Thurman Pedigo wrote: >Interesting point. I notice I have 4 devices. It's easy to decide on GTM and >DSM. Does this "nul" device serve any function in Cache/windows? It does >seem the Cache.dat versions are subject to a little variation. ...thx/t > > > $I: NUL ASK DEVICE: NO > ASK PARAMETERS: NO SIGN-ON/SYSTEM DEVICE: NO > LOCATION OF TERMINAL: Text Browser Utility > ASK HOST FILE: NO ASK HFS I/O OPERATION: NO > POST-CLOSE EXECUTE: D POSTCLS^RGEDBRS > PRE-OPEN EXECUTE: D PREOPEN^RGEDBRS SUBTYPE: P-RGBROWSER > TYPE: HOST FILE SERVER --------------------------------------- Jim Self Systems Architect, Lead Developer VMTH Computer Services, UC Davis (http://www.vmth.ucdavis.edu/us/jaself) ------------------------------------------------------- This SF.Net email is sponsored by Yahoo. Introducing Yahoo! Search Developer Network - Create apps using Yahoo! Search APIs Find out how you can build Yahoo! directly into your own Applications - visit http://developer.yahoo.net/?fr=offad-ysdn-ostg-q22005 _______________________________________________ Hardhats-members mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/hardhats-members
