# Keyword Reference

# #include-once

Specifies that the current file should only be included once.

#include-once

## Remarks

It is quite common to have the same "#include <filename.au3>" line in several of the files included in a script. If the same file were to be included several times, it is quite likely that this would generate a "Duplicate function" or "Cannot redeclare a Const" error. So when writing a script intended for use as an include file, add #include-once to prevent that file from being included more than once. Note that the #include-once line must be placed at the top of the script and before any other #include lines.
It is not recommended to add a #include-once line to scripts which are not intended to be used as include files within other scripts.

## Related

#include

## Example

    ; Use #include-once when creating UDFs so the file isn't included multiple times
    ; if you call the same UDF in multiple files.

    #include-once

    #include <MsgBoxConstants.au3>

    ; Add #include "Include-once.au3" at the top of your script.
    ; Then your script can call IncludeFunc().
    ; The execution will display a MsgBox.

    Func IncludeFunc()
        MsgBox($MB_SYSTEMMODAL, "", "This is an example of including a file.")
    EndFunc   ;==>IncludeFunc