This asynchronous function reads the values, qualities, timestamps, user ID, and timestamp of the modification from the history database for the specified time domain for one or more items.
The purpose of this function is to read values from history that have been modified/replaced (a value was returned with a quality of OPCHDA_EXTRADATA, indicating that there were other values for that item/timestamp which had been superseded).
The results are returned via the client's ReadModifiedComplete event handler.
Overload List
| Overload | Description |
|---|---|
| ReadModified(Int32,OPCHDAtime,OPCHDAtime,Int32,Int32[],Int32,Int32[]) | This asynchronous function reads the values, qualities, timestamps, user ID, and timestamp of the modification from the history database for the specified time domain for one or more items. The purpose of this function is to read values from history that have been modified/replaced (a value was returned with a quality of OPCHDA_EXTRADATA, indicating that there were other values for that item/timestamp which had been superseded). The results are returned via the client's ReadModifiedComplete event handler. |
| ReadModified(OPCHDAtime,OPCHDAtime,Int32,Int32[],OPCHDAmodifiedItem[],Int32[]) | This synchronous function reads the values, qualities, timestamps, user ID, and timestamp of the modification from the history database for the specified time domain for one or more items. The purpose of this function is to read values from history that have been modified/replaced. If ReadRaw, ReadProcessed, or ReadAtTime has returned a quality of OPCHDA_EXTRADATA, indicating that there are values which have been superseded, this function reads those values which were superseded. Only values that have been modified/replaced or deleted are read by this function. |
Requirements
Target Platforms: Windows 7/8/10, Windows Server 2008/2012/2016, .NET 4.x