_OFFSET (function) - QB64Official/qb64 GitHub Wiki

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 DECLARE 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 Variable Types 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.**

Example(s)

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