read_existing_point, read_point

Gamma: Version 4.0
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# `read_existing_point`, `read_point`

`read_existing_point`, `read_point` -- retrieve points.

## Syntax

    read_existing_point (symbol)
    read_point (symbol)

## Arguments

`symbol`

  A point name, as a symbol.

## Returns

The value of a point in the Cascade DataHub. If the point is unavailable then nil is returned. For `read_existing_point`, if the point does not exist than nil is returned. For `read_point`, if the point does not exist then the point is created and a default value is returned.

## Description

These functions makes a call to the Cascade DataHub to retrieve the point whose name is the same as the `symbol`. If the point does not exist in the datahub, `read_existing_point` returns nil and does not create the point. `read_point` will create a point in the datahub if necessary, whose value and confidence are both zero. If the point name is pre-qualified with a domain name and a colon (:), this function will search that domain's datahub rather than the datahub for the default domain.

## Example

This example uses data points entered in the `write_point` reference entry example.

        Gamma> init_ipc("reader","rq");
        t
        Gamma> read_point(#my);
        600
        Gamma> read_point(#dog);
        130
        Gamma> read_point(#has);
        140
        Gamma> read_point(#fleas);
        150
        Gamma> read_existing_point(#cat);
        nil
        Gamma> read_point(#cat);
        0
        Gamma>

## See Also

`register_point`, `write_point`

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