Delphi Basics : FreeMem command

DelphiBasics

FreeMem
Procedure

Free memory storage used by a variable

System unit

procedure FreeMem(MemoryPointer Pointer {; MemorySize Integer});

Description

The FreeMem procedure frees up memory storage used by a variable MemoryPointer.

You can optionally specify the MemorySize to be freed. However, you must specify the size allocated in the first place.

If the variable is nil then nothing happens.

If the variable invalidly points to memory (maybe it has already been freed), then an EInvalidPointer exception is thrown.

If the memory contains references to memory based variables, you must call Finalize before FreeMem.

FreeMem is the counter command to GetMem.

Ideally, you should use New and Dispose instead of GetMem and FreeMem. It avoids the need to call Finalize.

Related commands

Dispose		Dispose of storage used by a pointer type variable
GetMem		Get a specified number of storage bytes
New		Create a new pointer type variable
ReallocMem		Reallocate an existing block of storage

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Example code : A simple exampl of using GetMem and FreeMem

var
  charPtr  : PChar;

begin
  // Allocate storage for 4 characters
  GetMem(charPtr, 4 * SizeOf(Char));

  // Assign to these characters
  charPtr^ := 'A';
  Inc(charPtr);
  charPtr^ := 'B';
  Inc(charPtr);
  charPtr^ := 'C';
  Inc(charPtr);
  charPtr^ := #0;  // String terminator

  // Now display these values
  Dec(charPtr, 3);
  ShowMessage('Characters stored = '+charPtr);

  // Now free the memory for these characters
  FreeMem(charPtr);
end;

Show full unit code

Characters stored = ABC