Delphi Basics : GetMem command

DelphiBasics

GetMem
Function

Get a specified number of storage bytes

System unit

function GetMem(var StoragePointer Pointer; StorageSize Integer);

Description

The GetMem procedure attempts to get the specified StorageSize bytes of storage, storing a pointer to the storage in StoragePointer.

If the allocation fails, then a EOutOfMemory exception is raised.

The storage is not initialised in any way.

Notes

The GetMem procedure is Thread safe as long as IsMultiThread is true.

It is better to use New to allocate storage for records - the example is for illustration of GetMem and pointer manipulation.

Related commands

Dispose		Dispose of storage used by a pointer type variable
FillChar		Fills out a section of storage with a fill character or byte value
FreeMem		Free memory storage used by a variable
New		Create a new pointer type variable
ReallocMem		Reallocate an existing block of storage

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Example code : Get storage for 3 records and use this storage

type
  TRecord = Record
    name : string[10];
    age  : Byte;
  end;

var
  recPointer : ^TRecord;

begin
  // Allocate storage for three records
  // Note : It is better to use New for this
  // It is used here for illustration purposes only
  GetMem(recPointer, 3 * SizeOf(TRecord));

  // Fill out these 3 records with values
  recPointer.name := 'Brian';
  recPointer.age  := 23;

  Inc(recPointer);
  recPointer.name := 'Jim';
  recPointer.age  := 55;

  Inc(recPointer);
  recPointer.name := 'Sally';
  recPointer.age  := 38;

  // Now display these values
  Dec(recPointer, 2);
  ShowMessageFmt('%s is %d',[recPointer.name, recPointer.age]);
  Inc(recPointer);
  ShowMessageFmt('%s is %d',[recPointer.name, recPointer.age]);
  Inc(recPointer);
  ShowMessageFmt('%s is %d',[recPointer.name, recPointer.age]);
end;

Show full unit code

  Brian is 23
  Jim is 55
  Sally is 38