Delphi in a Nutshell

Name

GetMem Procedure

Syntax

procedure GetMem(var P: Pointer; Size: LongInt);

Description

GetMem allocates Size bytes of dynamic memory and stores a pointer to the memory in P. It does not initialize the allocated memory. GetMem is not a real procedure.

Tips and Tricks

• The memory that GetMem allocates is not initialized. If you are allocating strings, dynamic arrays, or Variants, you should call Initialize or set the memory to zero with FillChar.

• GetMem in Delphi’s default memory manager is thread-safe, that is, you can call GetMem from multiple threads simultaneously, but only if IsMultiThread is True.

• If you are allocating a record or fixed-size array, call New instead of GetMem.

• A common use for GetMem is to allocate an array where you do not know the array size at compile time. Although dynamic arrays have largely replaced the need for this trick, it is still commonly found in legacy Delphi code.

Example

// Create a grayscale palette, and return the palette handle.
// Although you can create a palette with up to 255 shades of gray,
// many video adapters can display only 15 or 16 bits per pixel,
// which means 5 bits per gray shade, or 32 distinct shades of gray.
function CreateGrayScalePalette(NumShades: Bytes);
var
  LogPalette: PLogPalette;
  I: Integer;
begin
  // TLogPalette already has room for one palette entry, so allocate
  // room for NumShades-1 additional palette entries.
  GetMem(LogPalette,
         SizeOf(TLogPalette) + (NumShades-1)*SizeOf(TPaletteEntry)); try LogPalette.palVersion ...