$INCLUDEONCE: Difference between revisions

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{{PageAvailability}}
{{PageExamples}}
;* Example: Show how the command prevents included code to be injected multiple times.
;* Example: Show how the command prevents included code to be injected multiple times.
:* First save the include files in your qb64pe folder, then take the main program.
:* First save the include files in your qb64pe folder, then take the main program.


{{Text|'''Save as "incl.bm"'''|black}}
<center>{{Text|'''Save as "incl.bm"'''|black}}</center>
{{CodeStart}}
{{CodeStart}}
{{Text|<nowiki>'included 2 times by test.bas</nowiki>|#919191}}
{{Text|<nowiki>'included 2 times by test.bas</nowiki>|#919191}}
Line 41: Line 41:
{{CodeEnd}}
{{CodeEnd}}


{{Text|'''Save as "once.bm"'''|black}}
<center>{{Text|'''Save as "once.bm"'''|black}}</center>
{{CodeStart}}
{{CodeStart}}
{{Text|<nowiki>'included by test.bas and incl.bm</nowiki>|#919191}}
{{Text|<nowiki>'included by test.bas and incl.bm</nowiki>|#919191}}
Line 51: Line 51:
{{CodeEnd}}
{{CodeEnd}}


{{Text|'''Save as "test.bas"'''|black}}
<center>{{Text|'''Save as "test.bas"'''|black}}</center>
{{CodeStart}}
{{CodeStart}}
{{Text|<nowiki>'this is a test for $INCLUDEONCE behavior</nowiki>|#919191}}
{{Text|<nowiki>'this is a test for $INCLUDEONCE behavior</nowiki>|#919191}}

Revision as of 14:57, 8 February 2024

The $INCLUDEONCE metacommand, when placed in include files, prevents that the file's contents is injected multiple times into a program, even if the file is included multiple times directly or indirectly through other include files.


Syntax

$INCLUDEONCE


Description

  • Aa QB64 metacommand it does not require a comment ' or REM before it.
  • It can be placed everywhere in an include file, but must be the only thing in the line, hence whithout additional whitespace or comments.
    • Even if placed in the middle or the end of the file, it always designates the entire file contents.
  • If placed in the main program, $INCLUDEONCE does nothing and is simply ignored without error.
  • $INCLUDEONCE will not work if placed inside pre-compiler $IF..$ELSE...$END IF blocks.


Availability


Examples

Example
  • Show how the command prevents included code to be injected multiple times.
  • First save the include files in your qb64pe folder, then take the main program.
Save as "incl.bm"
'included 2 times by test.bas

PRINT
PRINT "This prints from file incl.bm, it should appear 2 times on screen."

'$INCLUDE: 'once.bm'
Save as "once.bm"
'included by test.bas and incl.bm

$INCLUDEONCE

PRINT
PRINT "This prints from file once.bm, and should appear only once on screen."
Save as "test.bas"
'this is a test for $INCLUDEONCE behavior

PRINT "This prints from the test.bas main program."

'$INCLUDE: 'incl.bm'
'$INCLUDE: 'once.bm'
'$INCLUDE: 'incl.bm'

END


See also



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