System.FreeMem Function

Disposes of a dynamic variable of a given size.

Pascal

procedure FreeMem(var P: Pointer); overload;
procedure FreeMem(var P: Pointer; Size: Integer); overload;

C++

FreeMem(void * P);
FreeMem(void * P, int Size);

File

System

Description

In Delphi code, FreeMem destroys the variable referenced by P and returns its memory to the heap. If P does not point to memory in the heap, a runtime error occurs. If P points to a structure that includes long strings, variants, dynamic arrays, or interfaces, call Finalize before calling Freemem.

P is a variable of any pointer type previously assigned by the GetMem procedure.

Size specifies the size in bytes of the dynamic variable to dispose of; if specified, it must be exactly the number of bytes previously allocated to that variable by GetMem.

After calling FreeMem, the value of P is undefined.

Note: It is preferable to use the New and Dispose procedures rather than GetMem and FreeMem. When using New and Dispose, there is no need to explicitly call Finalize.

Delphi Examples:

Copy Code

{
The following example uses a button, a string grid, and an
Open dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the specified file is opened, read into a buffer, and closed.
Then the buffer is displayed in two columns of the string
grid. The first column contains the character values in the
buffer. The second column contains the numeric values of the
characters in the buffer.
} 
procedure TForm1.Button1Click(Sender: TObject);
var
  iFileHandle: Integer;
  iFileLength: Integer;
  iBytesRead: Integer;
  Buffer: PChar;
  i: Integer;
begin
  if OpenDialog1.Execute then
  begin
    try
      iFileHandle := SysUtils.FileOpen(OpenDialog1.FileName, fmOpenRead);
      iFileLength := SysUtils.FileSeek(iFileHandle,0,2);
      FileSeek(iFileHandle,0,0);
      Buffer := PChar(System.AllocMem(iFileLength + 1));
      iBytesRead := SysUtils.FileRead(iFileHandle, Buffer^, iFileLength);
      FileClose(iFileHandle);
      for i := 0 to iBytesRead-1 do
      begin
        StringGrid1.RowCount := StringGrid1.RowCount + 1;
        StringGrid1.Cells[1,i+1] := Buffer[i];
        StringGrid1.Cells[2,i+1] := IntToStr(Integer(Buffer[i]));
      end;
    finally
      FreeMem(Buffer);
    end;
  end;
end;