Nested Exceptions Code executed in an exception handler can itself raise and handle exceptions. As long as these exceptions are also
handled within the exception handler, they do not affect the original exception. However, once an exception raised
in an exception handler propagates beyond that handler, the original exception is lost. This is illustrated by the Tan
function below.
type
ETrigError = class(EMathError);
function Tan(X: Extended): Extended;
begin
try
Result := Sin(X) / Cos(X);
except
on EMathError do
raise ETrigError.Create('Invalid argument to Tan');
end;
end;
If an EMathError exception occurs during execution of Tan, the exception handler raises an
ETrigError
. Since
Tan does not provide a handler for
ETrigError
, the exception propagates beyond the original exception handler,
causing the EMathError exception to be destroyed. To the caller, it appears as if the Tan function has raised an
ETrigError
exception.
