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48 lines
2.3 KiB
Plaintext
48 lines
2.3 KiB
Plaintext
The '''BYVAL''' statement is used to pass a parameter's value with {{KW|SUB}} programs made in other programming languages.
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{{PageSyntax}}
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:: Procedure_Name ('''BYVAL''' ''variable1'', '''BYVAL''' ''variable2'')
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{{PageDescription}}
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* QB64 supports keyword only with [[DECLARE LIBRARY]] [[SUB]] and [[FUNCTION]] procedure declarations.
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* Passing by value assures that the original variable value is not changed by another procedure.
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* '''QB64''' can use BYVAL in [[DECLARE LIBRARY]] procedures that add SDL libraries or DLL functions.
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* Use [[parenthesis]] around [[SUB]] or [[FUNCTION]] parameters passed BY VALUE in Qbasic or QB64. Ex: ''CALL Procedure ((x&), (y&))''
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* Qbasic versions below 7 do not use {{KW|BYVAL}} unless the {{KW|SUB}} program referred to is from a different programming language.
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* PDS versions can use {{KW|BYVAL}} as it is intended in any {{KW|SUB}} or {{KW|FUNCTION}} parameters.
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*'''BYVAL''' can also be used with [[ABSOLUTE]] in Qbasic but not in QB64 currently.
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* '''NOTE: Many Qbasic keyword variable names CAN be used with a [[STRING]] suffix($) ONLY! You CANNOT use them without the suffix, use a numerical suffix or use [[DIM]], [[REDIM]], [[_DEFINE]], [[BYVAL]] or [[TYPE]] variable [[AS]] statements!'''
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''Example:'' Passing parameters "by value" using [[parenthesis|brackets]] when calling a [[SUB]] or [[FUNCTION]] in Qbasic or QB64.
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{{CodeStart}} '' ''
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{{Cl|CALL}} MySUB (a%, (b%), (c%)) 'CALL SUB
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MySUB a%, b%, (c%) 'call SUB again without CALL
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{{Cl|PRINT}} "Outside procedure: "; a%, b%, c%
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{{Cl|SUB}} MySUB (a%, b%, c%)
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a% = a% + 1: b% = b% + 1: c% = c% + 1
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{{Cl|PRINT}} "Inside procedure: "; a%, b%, c%
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{{Cl|END SUB}} '' ''
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{{CodeEnd}}
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{{OutputStart}}
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Inside procedure: 1 1 1
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Inside procedure: 2 1 1
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Outside procedure: 2 1 0
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{{OutputEnd}}
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:''Explanation:'' Both SUB calls pass just the '''values''' of b% and c% to the procedure. The first variable, a%, is passed by '''reference''' (the default) so the value was changed by the SUB procedure. Brackets can only be used in the [[CALL]] or function reference!
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{{PageSeeAlso}}
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* [[DECLARE LIBRARY]]
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* [[SUB]], [[FUNCTION]]
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* [[DECLARE]], [[DECLARE (non-BASIC statement)]]
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* [[CALL]]
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* [[Libraries#C++_Variable_Types|C++ Variable Types]]
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{{PageNavigation}} |