OFFSET (function): Difference between revisions
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* Returns the memory offset of variables, user-defined-types & elements, arrays & indices and the base offset of [[STRING]]s. | * 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 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. | * OFFSET values are used as a part of the [[_MEM]] variable [[Variable Types|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.''' | * '''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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''Example:'' Using memcpy with the _OFFSET function values as parameters. | ''Example:'' Using memcpy with the _OFFSET function values as parameters. | ||
{{CodeStart}} | {{CodeStart}} | ||
{{Cl|DECLARE | {{Cl|DECLARE 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|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}} | {{Cl|DECLARE LIBRARY|END DECLARE}} | ||
| Line 37: | Line 37: | ||
* [[_OFFSET]] | * [[_OFFSET]] | ||
* [[DECLARE LIBRARY]] | * [[DECLARE LIBRARY]] | ||
* [[DECLARE | * [[DECLARE LIBRARY]] | ||
* [[Using _OFFSET]] | * [[Using _OFFSET]] | ||
{{PageNavigation}} | {{PageNavigation}} | ||
Latest revision as of 23:01, 27 February 2024
The _OFFSET function returns the memory offset of/within a given variable.
Syntax
- offset%& = _OFFSET(variable)
Description
- The variable parameter can be any type of numerical or string variable name.
- API LIBRARY parameter or 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 STRINGs.
- 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; 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.
Examples
Example: Using memcpy with the _OFFSET function values as parameters.
DECLARE CUSTOMTYPE LIBRARY SUB memcpy (BYVAL dest AS _OFFSET, BYVAL source AS _OFFSET, BYVAL bytes AS LONG) END DECLARE a$ = "1234567890" b$ = "ABCDEFGHIJ" memcpy _OFFSET(a$) + 5, _OFFSET(b$) + 5, 5 PRINT a$ |
12345FGHIJ |
See also