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45 lines
2.1 KiB
Plaintext
45 lines
2.1 KiB
Plaintext
{{DISPLAYTITLE:_OFFSET (function)}}
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The [[_OFFSET]] function returns the memory offset of/within a given variable.
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{{PageSyntax}}
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: {{Parameter|offset%&}} = [[_OFFSET]]({{Parameter|variable}})
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{{PageDescription}}
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* The {{Parameter|variable}} parameter can be any type of numerical or [[STRING|string]] variable name.
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* API [[DECLARE LIBRARY|LIBRARY]] parameter or [[TYPE|type]] names may include '''lp, ptr''' or '''p''' which designates them as a pointer type.
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* _OFFSET function return values should be stored in [[_OFFSET]] type variables. As no other variable type is 'elastic' like [[_OFFSET]], there can be no guarantee that any other variable type can hold the value of an _OFFSET.
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* Returns the memory offset of variables, user-defined-types & elements, arrays & indices and the base offset of [[STRING]]s.
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* Offset values are currently only useful when used in conjunction with [[_MEM]] or [[DECLARE LIBRARY]] procedures.
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* OFFSET values are used as a part of the [[_MEM]] variable [[type]] in QB64; {{Parameter|variable}}.OFFSET returns or sets the current position in memory.
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* '''Warning:''' QB64 variable length strings can move about in memory at any time. If you get the _OFFSET of a variable length sting on one line and use it on the next it may not be there anymore.''' To be safe, move variable length strings into fixed length strings first.'''
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{{PageExamples}}
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''Example:'' Using memcpy with the _OFFSET function values as parameters.
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{{CodeStart}} '' ''
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{{Cl|DECLARE DYNAMIC LIBRARY|DECLARE CUSTOMTYPE LIBRARY}}
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{{Cl|SUB}} memcpy ({{Cl|BYVAL}} dest {{Cl|AS}} {{Cl|_OFFSET}}, {{Cl|BYVAL}} source {{Cl|AS}} {{Cl|_OFFSET}}, {{Cl|BYVAL}} bytes {{Cl|AS}} {{Cl|LONG}})
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{{Cl|DECLARE LIBRARY|END DECLARE}}
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a$ = "1234567890"
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b$ = "ABCDEFGHIJ"
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memcpy {{Cl|_OFFSET (function)|_OFFSET}}(a$) + 5, {{Cl|_OFFSET (function)|_OFFSET}}(b$) + 5, 5
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{{Cl|PRINT}} a$ '' ''
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{{CodeEnd}}
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{{OutputStart}}12345FGHIJ
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{{OutputEnd}}
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{{PageSeeAlso}}
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* [[_OFFSET]] {{text|(variable type)}}
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* [[DECLARE LIBRARY]]
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* [[DECLARE DYNAMIC LIBRARY]]
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* [[Using _OFFSET]]
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{{PageNavigation}}
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