bstr_data_point_get_value(3) — Subroutines

Name

bstr_data_point_get_value − Reads the value of a Data_Point (VODB only).

Syntax

bstr_t_status   bstr_data_point_get_value (
                                  bstr_t_reference ∗data_point,
                                  bstr_t_boolean   read source,
                                  bstr_t_rcb       ∗control,
                                  bstr_t_value     ∗value);

Description

The bstr_data_point_get_value procedure returns in value the current value of the Data_Point specified by data_point.

Applications can read the current values of simple and complex Data_Point objects by means of a single call to the bstr_data_point_get_value procedure.

In addition, if the Data_Point is linked as consumer to a producer Data_Point, the access_producer argument can force Data Services to read the current value of the producer Data_Point.

Arguments

data_point
access: read
The reference to the Data_Point.

access_producer
access: read
This argument is only significant if both of the following conditions are met:

•The value of the access_policy attribute of data_point is set to ON_REQUEST.

•The data_point Data_Point is linked as consumer to a producer Data_Point, or is an External_Data_Point with the external_behavior attribute set to PRODUCER.

Under these conditions, the access_producer argument informs Data Services whether the current value of the producer Data_Point is to be accessed. The following values are permitted for this argument:

•BSTR_C_TRUE. Data Services is forced to read the value of the producer Data_Point, overriding any value specified in the update_policy and access_policy attributes.

•BSTR_C_FALSE. The current value of the Data_Point itself is read without the value of the producer Data_Point being accessed.

control
access: read
The address of an optional request control block.

value
access: write
The address of a buffer where the Data_Point’s current value is returned. The buffer allocated by the caller must be consistent with the datatype of the Data_Point to be read.

Return Values

BSTR_S_ABORTED	Operation aborted
BSTR_S_BAD_PARAMETER	Bad parameter value
BSTR_S_BAD_REFERENCE	Bad reference
BSTR_S_COMMUNICATION_ERROR	Communication error
BSTR_S_COM_PC_SIZE_MISMATCH	Number of bytes requested does not match the number of bytes returned
BSTR_S_DEVICE_SERVICES_NOT_AVAILABLE	Device Services are not available
BSTR_S_EXPIRED	The lifetime of the Data_Point’s value has expired
BSTR_S_FINISH	Request aborted by bstr_finish
BSTR_S_INTERNAL_ERROR	Internal error
BSTR_S_INTR	Operation interrupted
BSTR_S_INVALID_OPERATION	Invalid operation
BSTR_S_INVALID_RCB	Invalid Request Control Block
BSTR_S_INVALID_USAGE	Invalid reference usage
BSTR_S_NORMAL	Normal successful completion
BSTR_S_NO_MEMORY	Insufficient virtual memory
BSTR_S_OBJECT_NOT_IN_SET	The variable is not in the locked set
BSTR_S_SERVER_NOT_REACHABLE	Server not reachable
BSTR_S_TIMEOUT	Timeout expired
BSTR_S_TOO_MANY_REQUESTS	Too many pending requests

Museum