21.2.Return Syntax

When the OPC DataHub executes a command, it may return a success message or an error message. The returned message contains the original command, and some or all of the arguments for the command. These messages will be received by programs using the DataHub APIs for C++, Java, and .NET, but they will not be received by DataHub scripts. The two types of success messages are:

Success messages are returned if the DataHub command acksuccess has been previously issued with a value of 1. A value of 0 means no success messages will be returned. Error messages are returned any time there is an error. There are four types of error messages:

The error messages are the negation of these error codes:

ST_OKThe function executed without error.
ST_ERRORAn error occurred.
ST_NO_TASKA required task does not exist.
ST_NO_MSGThere is no message available.
ST_WOULDBLOCKThis action would block, and is not permitted.
ST_INTRAn interrupt occurred.
ST_FULLThe queue is full.
ST_LOCKEDA DataHub point is locked.
ST_SECURITYThe security level is insufficient.
ST_NO_POINTA required DataHub point does not exist.
ST_INSIGA change in a DataHub point's value is insignificant. This is not really an error, but a notification that no exception will be generated by the datahub.
ST_UNKNOWNThere is an unknown error.
ST_NO_QUEUEA target task has no queue, or qserve is absent.
ST_CMD_SYNTAX_ERRORThe command was not found, or there was a syntax error.
ST_REPLIEDThe reply was complete.
ST_WRONG_TYPEThe type of a point or variable was wrong.
ST_TOO_LARGEA value to be written to memory is larger than the available buffer.
ST_NO_MEMORYThere is insufficient memory available.
ST_OLD_DATATime-significant data is out of date.
ST_TIMEOUTA timeout occurred in poll mode.