write_existing_point, write_point

Gamma: Version 4.0
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# `write_existing_point`, `write_point`

`write_existing_point`, `write_point` -- write point values.

## Syntax

    write_existing_point (symbol, value, seconds?, nanoseconds?)
    write_point (symbol, value, seconds?, nanoseconds?)

## Arguments

`symbol`

  A point name, as a symbol.

`value`

  Any numeric or string expression.

`seconds`

  Number of seconds since Jan 1st, 1970.

`nanoseconds`

  Number of nanoseconds within the second.

## Returns

t on success or nil on failure.

## Description

These functions write a point value to the Cascade DataHub. If the point does not exist in the datahub, `write_point` will create the point and set its value. `write_existing_point` will return nil if the point does not exist.

## Example

        Gamma> init_ipc("writer","wq");
        t
        Gamma> write_existing_point("my",150);
        nil
        Gamma> write_point(#my,120);
        t
        Gamma> write_point(#dog,130,450000000);
        t
        Gamma> write_point("has",140);
        t
        Gamma> write_point("fleas",150,1210947,2134444);
        t
        Gamma> write_existing_point("my",600);
        t
        Gamma>

These points can be viewed in the datahub (sorted in alphabetical order) using the dhview command at the shell prompt:

        #     Point Name            Conf Value
        1     dog                   100  130
        2     fleas                 100  150
        3     has                   100  140
        4     my                    100  600

See the The PID Controller Class section of the PID Emulator chapter, or the Update Functions section of the GTK Functions chapter (Tutorial One), or the Button Functions section of the Photon Functions chapter (Tutorial One) in the Cogent Tools Demo and Tutorials book for examples of this function used in context.

## See Also

`read_point`, `read_existing_point`, `register_point`

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