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47 lines
1.8 KiB
Markdown
47 lines
1.8 KiB
Markdown
The [_OFFSET](_OFFSET) function returns the memory offset of/within a given variable.
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## Syntax
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> offset%& = [_OFFSET](_OFFSET)(variable)
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## Description
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* The variable parameter can be any type of numerical or [STRING](STRING) variable name.
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* API [DECLARE LIBRARY](DECLARE-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](_OFFSET) type variables. As no other variable type is 'elastic' like [_OFFSET](_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](STRING)s.
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* Offset values are currently only useful when used in conjunction with [_MEM](_MEM) or [DECLARE LIBRARY](DECLARE-LIBRARY) procedures.
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* OFFSET values are used as a part of the [_MEM](_MEM) variable [Variable Types](Variable-Types) in QB64; 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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## Example(s)
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Using memcpy with the _OFFSET function values as parameters.
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```vb
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DECLARE CUSTOMTYPE LIBRARY
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SUB memcpy (BYVAL dest AS _OFFSET, BYVAL source AS _OFFSET, BYVAL bytes AS LONG)
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END DECLARE
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a$ = "1234567890"
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b$ = "ABCDEFGHIJ"
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memcpy _OFFSET(a$) + 5, _OFFSET(b$) + 5, 5
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PRINT a$
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```
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```text
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12345FGHIJ
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```
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## See Also
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* [_OFFSET](_OFFSET) (variable type)
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* [DECLARE LIBRARY](DECLARE-LIBRARY)
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* [DECLARE DYNAMIC LIBRARY](DECLARE-DYNAMIC-LIBRARY)
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* [Using _OFFSET](Using--OFFSET)
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