System.AcquireExceptionObject Function

Retains access to exception object.

Pascal

function AcquireExceptionObject: Pointer;

C++

void * AcquireExceptionObject();

File

System

Description

AcquireExceptionObject returns a pointer to the current exception object and prevents the exception object from being deallocated when the current exception handler exits.

Note: AcquireExceptionObject increments the exception object's reference count. Make sure that the reference count is decremented when the exception object is no longer needed. This happens automatically if you use the exception object to re-raise the exception. In all other cases, every call to AcquireExceptionObject must have a matching call to ReleaseExceptionObject. AcquireExceptionObject/ReleaseExceptionObject sequences can be nested.

Delphi Examples:

Copy Code

{
This example demonstrates exception handling to catch runtime
errors.
}

procedure TForm2.btIOErrorClick(Sender: TObject);
var
  ExceptionObj : TObject;
begin
  {
  Try to write something onto the console - will raise an
  exception.
  }
  try
  WriteLn('This will generate an error because there is no' +
          ' console attached!');
  except
    ExceptionObj := ExceptObject;
    if ExceptionObj = nil then
      MessageDlg('No exception', mtError, [mbOK], 0)
    else
    begin
      MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0);
    end;
  end;
end;

{$OVERFLOWCHECKS ON}
{$OPTIMIZATION OFF}
{$HINTS OFF}
procedure TForm2.btOverflowErrClick(Sender: TObject);
var
  b : Cardinal;
  ExceptionPtr : Pointer;
begin
  {
  Simulate an overflow: Note, enabled the overflow
  checking and disabled optimizations because Delphi's
  compiler will not compile this code otherwise.
  }
  ExceptionPtr := nil;
  try
    b := $FFFFFFFF;
    b := b * b;
  except
    ExceptionPtr := AcquireExceptionObject;
  end;

  // Check exception
  if ExceptionPtr = nil then
    MessageDlg('No exception', mtError, [mbOK], 0)
  else
  begin
    MessageDlg(TObject(ExceptionPtr).ToString, mtError, [mbOK], 0);
    ReleaseExceptionObject;
  end;
end;
{$HINTS ON}
{$OPTIMIZATION ON}
{$OVERFLOWCHECKS OFF}

procedure TForm2.btRuntimeErrorClick(Sender: TObject);
var

  ExceptionObj : TObject;
  begin
  { Simulate an access violation }
  try
    System.Error(reAccessViolation);
  except
    ExceptionObj := ExceptObject;
    if ExceptionObj = nil then
      MessageDlg('No exception', mtError, [mbOK], 0)
    else
    begin
      MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0);
    end;
  end;
end;

procedure TForm2.FormCreate(Sender: TObject);
begin

end;