$INCLUDEONCE: Difference between revisions
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Save as "once.bm"
Save as "incl.bm"
Save as "test.bas"
If it works, the output looks like this...
Examples by RhoSigma
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{{PageDescription}} | {{PageDescription}} | ||
* As QB64 [[metacommand]] it does not require a comment ''[[Apostrophe|']]'' or [[REM]] before it. | * As QB64 [[metacommand]] it does not require a comment ''[[Apostrophe|']]'' or [[REM]] before it. | ||
* It can be placed everywhere in an include file, but must be the '''only''' thing in the line, hence | * It can be placed everywhere in an include file, but must be the '''only''' thing in the line, hence without additional whitespace or comments. | ||
** Even if placed in the middle or the end of the file, it always designates the '''entire''' file contents. | ** Even if placed in the middle or the end of the file, it always designates the '''entire''' file contents. | ||
* If placed in the main program, '''$INCLUDEONCE''' does nothing and is simply ignored without error. | * If placed in the main program, '''$INCLUDEONCE''' does nothing and is simply ignored without error. | ||
* '''$INCLUDEONCE''' will not work | * '''$INCLUDEONCE''' will not work when placed inside pre-compiler [[$IF]]..[[$ELSE]]...[[$END IF]] blocks. | ||
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;* 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. | ||
<center>{{Text|'''Save as "once.bm"'''|black}}</center> | |||
{{CodeStart}} | |||
{{Text|<nowiki>'included by test.bas and incl.bm</nowiki>|#919191}} | |||
{{Cm|$INCLUDEONCE}} | |||
{{Cl|PRINT}} | |||
{{Cl|PRINT}} {{Text|<nowiki>"This prints from file once.bm, and should appear only once on screen."</nowiki>|#FFB100}} | |||
{{CodeEnd}} | |||
<center>{{Text|'''Save as "incl.bm"'''|black}}</center> | <center>{{Text|'''Save as "incl.bm"'''|black}}</center> | ||
| Line 39: | Line 49: | ||
{{Text|<nowiki>'</nowiki>|#919191}}{{Cm|$INCLUDE}}: {{Text|<nowiki>'once.bm'</nowiki>|#919191}} | {{Text|<nowiki>'</nowiki>|#919191}}{{Cm|$INCLUDE}}: {{Text|<nowiki>'once.bm'</nowiki>|#919191}} | ||
{{CodeEnd}} | {{CodeEnd}} | ||
| Line 63: | Line 63: | ||
{{Cl|END}} | {{Cl|END}} | ||
{{CodeEnd}} | {{CodeEnd}} | ||
<center>{{Text|'''If it works, the output looks like this...'''|black}}</center> | |||
{{OutputStart}} | |||
This prints from the test.bas main program. | |||
This prints from file incl.bm, it should appear 2 times on screen. | |||
This prints from file once.bm, and should appear only once on screen. | |||
This prints from file incl.bm, it should appear 2 times on screen. | |||
{{OutputEnd}} | |||
{{PreStart}} | |||
'''Explanation''' | |||
Even as the file ''once.bm'' is included 3 times into the ''test.bas'' program | |||
(2 times indirectly through ''incl.bm'' and 1 time directly), the contained | |||
PRINT statements are injected only once into the program due to the use | |||
of the $INCLUDEONCE metacommand. | |||
{{PreEnd}} | |||
{{Small|Examples by RhoSigma}} | |||
{{PageSeeAlso}} | {{PageSeeAlso}} | ||
* [https://qb64phoenix.com/forum/showthread.php?tid=2685 Featured in our "Keyword of the Day" series] | |||
* [[$INCLUDE]] | * [[$INCLUDE]] | ||
* [[Metacommand]] | * [[Metacommand]] | ||
Latest revision as of 22:45, 25 May 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
Description
- As 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 without 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 when placed inside pre-compiler $IF..$ELSE...$END IF blocks.
Availability
none
v3.12.0
yes
yes
yes
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.
'included by test.bas and incl.bm $INCLUDEONCE PRINT PRINT "This prints from file once.bm, and should appear only once on screen." |
'included 2 times by test.bas PRINT PRINT "This prints from file incl.bm, it should appear 2 times on screen." '$INCLUDE: 'once.bm' |
'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 |
This prints from the test.bas main program. This prints from file incl.bm, it should appear 2 times on screen. This prints from file once.bm, and should appear only once on screen. This prints from file incl.bm, it should appear 2 times on screen. |
Explanation Even as the file once.bm is included 3 times into the test.bas program (2 times indirectly through incl.bm and 1 time directly), the contained PRINT statements are injected only once into the program due to the use of the $INCLUDEONCE metacommand. |
See also