_MEMCOPY - QB64Official/qb64 GitHub Wiki

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

Syntax

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

Parameter(s)

  • 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.

Description

  • 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(s)

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...NEXT 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