From QB64 Wiki
Revision as of 12:40, 17 February 2021 by Odin (talk | contribs) (Text replacement - "{{Parameters}}" to "{{PageParameters}}")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

The _MEMCOPY statement copies a block of bytes from one memory offset to another offset in memory.


_MEMCOPY sourceBlock, sourceBlock.OFFSET, sourceBlock.SIZE TO destBlock, destBlock.OFFSET


  • sourceBlock is the source memory block name created AS _MEM.
  • sourceBlock.OFFSET is the dot _OFFSET within the source memory block to read from.
  • sourceBlock.SIZE is the total number of bytes to transfer based on actual size.
  • destBlock is the destination _MEM memory block name to transfer data to.
  • destBlock.OFFSET is the dot _OFFSET within the dest _MEM memory block to write to.


  • The dot OFFSET is the memory block's start location in memory. Add bytes to place data further into the block.
  • The dot SIZE is the total byte size of the memory block to transfer. You can transfer all or a portion of the data bytes.
  • The memory block regions may overlap.
  • Always free memory blocks after values have been transferred to variables and are no longer required.


Example: Swapping data from one STRING variable to another. Fixed length strings are recommended for speed.

DIM m AS _MEM DIM n AS _MEM m = _MEMNEW(10) n = _MEMNEW(100) _MEMPUT m, m.OFFSET, "1234567890" s$ = SPACE$(10) 'to load into a variable length string set its length first _MEMGET m, m.OFFSET, s$ PRINT "in:[" + s$ + "]" _MEMCOPY m, m.OFFSET, m.SIZE TO n, n.OFFSET 'put m into n b$ = SPACE$(10) _MEMGET n, n.OFFSET, b$ PRINT "out:[" + b$ + "]" _MEMFREE m: _MEMFREE n 'always clear the memory when done

Snippet: Instead of copying each array element, one at a time in nested FOR loops, _MEMCOPY does it in one statement instantly.

'copy array a to array b one index at a time: FOR i1 = 0 TO 100 FOR i2 = 0 TO 100 b(i1, i2) = a(i1, i2) NEXT NEXT 'copy array a to array b in memory instantly: DIM ma AS _MEM: ma = _MEM(a()) 'place array data into blocks DIM mb AS _MEM: mb = _MEM(b()) _MEMCOPY ma, ma.OFFSET, ma.SIZE TO mb, mb.OFFSET _MEMFREE ma: _MEMFREE mb 'clear the memory when done

See also

Keyword Reference - Alphabetical
Keyword Reference - By Usage
Main Wiki Page