hist_register

Cascade Historian: Version 4.1
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# `hist_register`

`hist_register` -- registers histories with the Cascade DataHub.

## Syntax

    hist_register (hist_task[, pattern])

## Parameters

`hist_task`

  The task object corresponding to the Cascade Historian. See `locate_task` in the Gamma manual.

`pattern`

  The name of one or more (using a globbing pattern) histories to be acted upon. When this parameter is not specified, the default is `*`, to include all histories.

## Returns

`t` (true) if successful. Otherwise returns `nil` and sets `_last_error_` to the error string returned by the Cascade Historian.

## Description

This function causes the Cascade Historian to register each history matching the pattern with the Cascade DataHub point of the same name. Any subsequent value changes transmitted by the Cascade DataHub will be treated exactly the same as if add or `HI_Add` were called with that history, value and timestamp. If a history has already been registered, this function does nothing. If the Cascade DataHub is not running, no registration occurs. If multiple histories are associated with the same point, registering or unregistering one of the histories will do the same to all the other histories sharing the same point.

A Cascade DataHub point is a unit of storage in the datahub. Points have a name (a string), a value (real, integer, or string), and a time associated with them. They can be written to the Cascade DataHub in a number of ways, including for example the Cascade DataHub writept command and the Gamma `write_point` function. The Cascade Historian receives a point's data from the Cascade DataHub by registering for it with the register command or `HI_Register` function.

This function corresponds to the register command, and the Cogent API function `HI_Register`.

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