System.AllocMem Function

AllocMem allocates a memory block and initializes each byte to zero.

Pascal

function AllocMem(Size: Cardinal): Pointer;

C++

void * AllocMem(unsigned Size);

File

System

Description

AllocMem allocates a block of the given Size on the heap, and returns the address of this memory. Each byte in the allocated buffer is set to zero. To dispose of the buffer, use FreeMem. If there isn't enough memory available to allocate the block, an EOutOfMemory exception is raised.

Note: If the memory does not need to be zero-initialized, it is more efficient to use GetMem instead.

C++ 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.
*/

#include <memory>       //for STL auto_ptr class

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  int iFileHandle;
  int iFileLength;
  int iBytesRead;
  char *pszBuffer;
  if (OpenDialog1->Execute())
  {
    try
    {
      iFileHandle = FileOpen(OpenDialog1->FileName, fmOpenRead);
      iFileLength = FileSeek(iFileHandle,0,2);
      FileSeek(iFileHandle,0,0);
//    pszBuffer = PChar(AllocMem(iFileLength+1));
      std::auto_ptr<char> pszBuffer(new char[iFileLength+1]);
      iBytesRead = FileRead(iFileHandle, pszBuffer.get(), iFileLength);
      FileClose(iFileHandle);
      for (int i=0;i<iBytesRead;i++)
      {
        StringGrid1->RowCount += 1;
        StringGrid1->Cells[1][i+1] = pszBuffer.get()[i];
        StringGrid1->Cells[2][i+1] = IntToStr((int)pszBuffer.get()[i]);
      }
    }
    catch(...)
    {
      Application->MessageBox(
        L"Can't perform one of the following file operations: Open, Seek, Read, Close.",
        L"File Error", IDOK);
    }
  }
}

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: PAnsiChar;
  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 := 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;