QB64-PE/internal/help/_OFFSET_(function).txt

{{DISPLAYTITLE:_OFFSET (function)}}
The [[_OFFSET]] function returns the memory offset of/within a given variable.


{{PageSyntax}}
: {{Parameter|offset%&}} = [[_OFFSET]]({{Parameter|variable}})


{{PageDescription}}
* The {{Parameter|variable}} parameter can be any type of numerical or [[STRING|string]] variable name.
* API [[DECLARE LIBRARY|LIBRARY]] parameter or [[TYPE|type]] names may include '''lp, ptr''' or '''p''' which designates them as a pointer type.
* _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.
* Returns the memory offset of variables, user-defined-types & elements, arrays & indices and the base offset of [[STRING]]s.
* Offset values are currently only useful when used in conjunction with [[_MEM]] or [[DECLARE LIBRARY]] procedures. 
* 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.
* '''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.'''


{{PageExamples}}
''Example:'' Using memcpy with the _OFFSET function values as parameters.
{{CodeStart}} '' ''
{{Cl|DECLARE DYNAMIC LIBRARY|DECLARE CUSTOMTYPE LIBRARY}}
    {{Cl|SUB}} memcpy ({{Cl|BYVAL}} dest {{Cl|AS}} {{Cl|_OFFSET}}, {{Cl|BYVAL}} source {{Cl|AS}} {{Cl|_OFFSET}}, {{Cl|BYVAL}} bytes {{Cl|AS}} {{Cl|LONG}})
{{Cl|DECLARE LIBRARY|END DECLARE}}

a$ = "1234567890"
b$ = "ABCDEFGHIJ"

memcpy {{Cl|_OFFSET (function)|_OFFSET}}(a$) + 5, {{Cl|_OFFSET (function)|_OFFSET}}(b$) + 5, 5
{{Cl|PRINT}} a$ '' ''
{{CodeEnd}}
{{OutputStart}}12345FGHIJ
{{OutputEnd}}


{{PageSeeAlso}}
* [[_OFFSET]] {{text|(variable type)}}
* [[DECLARE LIBRARY]]
* [[DECLARE DYNAMIC LIBRARY]]
* [[Using _OFFSET]]


{{PageNavigation}}
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