move

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The procedure Move (originated from Borland Pascal) copies data from one location in memory to another. Unlike the name suggests, no data is “lost” at the source. Its signature reads:

procedure Move(const source; var destination; count: sizeInt)

Note that source and destination do not have a data type, thus specifying an Identifier without (necessarily) applying the address‑operator is sufficient.

Application

Move can be considered a very “low-level” routine. It was originally developed to copy char values within the same string, but has ever since been (ab‑)used for other purposes, too:

  • If Pascal’s strong data type system imposes (too many) restrictions that need to be circumvented for hardware-close programming and typecasting does not resolve the task’s problem or is too cumbersome.
  • For circumventing Pascal’s restrictions in a very “hacky” nature: E. g. copying a file variable (there are good reasons you cannot simply := to a file).
  • For performance reasons: Copying huge blocks of memory with move could be faster than an equivalent for‑loop. For instance the x86‑64 implementation takes advantage of architecture-specific circumstances.
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Note: Using move often makes your code very unportable since it often makes assumptions about endianness, internal structures or similar things.

A quick demo should not be missing. Nevertheless, this example is bad in nature. A plain := assignment would have been sufficient. Note, using move possibly prevents the compiler from performing certain optimizations.

program moveDemo(input, output, stdErr);
var
	x, y: integer;
begin
	x := 42;
	move(x, y, sizeOf(x));
	writeLn(y);
end.

See also

  • moveChar0 - move until first chr(0) but at most count char values.
  • copy - creates a copy of data on the heap and returns a pointer to it.