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https://github.com/QB64-Phoenix-Edition/QB64pe.git
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6e01fc8dce
Added new _STRCMP and _STRICMP commands for quick string comparisons. Cleaned up QB64 to finish removing the QUI (quick user insert) code and folders. Altered UCASE and LCASE routines to be faster in some situations for us.
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}} |