Re: advice on best use of try catch throw

From:

Beman Dawes <bdawes@acm.org>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 08 Apr 2007 10:25:10 -0400

Message-ID:

<#Zd3pmeeHHA.4136@TK2MSFTNGP02.phx.gbl>

Bo Persson wrote:

mr.sir bossman wrote:
:: I am writing a windows wrapper class and I am wondering if I should
:: use try-catch-throw in this function...Or should I just return the
:: BOOL type and catch error at call with if()?
::
:: Any advice on this or a better way greatly appreciated. Thx ahead of
:: time. Note: Yes I've heard of MFC, ATL, WTL, etc and yes I know I
:: should just use them.
::
:: <in windows wrapper class>
:: //windows handle
:: HWND m_hWnd;
:: //CError is just wrapper around DWORD
:: CError m_cError;
::
:: void CloseWindow() throw(CError)
:: {
:: if(!(::IsWindow(m_hWnd)))
:: {
:: m_cError.SetError(INVALID_HANDLE);
:: throw(m_cError);
:: }
::
:: if(!(::CloseWindow(m_hWnd)))
:: {
:: m_cError.SetError(0);
:: throw(::GetLastError());
:: }
:: }
:: </in windows wrapper class>

I believe it depends on where the error is going to be handled. Is it the
routine calling CloseWindow() that will handle (sorry:-) the INVALID_HANDLE
problem? In that case, a return code is fine.

If this is a problem handled much higher up in the program structure, an
exception might simplify code at the intermediate levels. They will just
have to let the exception pass through, and will not have to test for and
propagate any return codes. This is especially handy for error conditions
that are really not expected to happen.

That's a good answer. Sometimes with API wrapper designs there are
important use cases for both returning error codes and throwing
exceptions, so both approaches have to be supported.

I've got a proposal pending to include better support in C++0x for error
handling from system API's. See
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2174.html A
Boost implementation will be available soon.

--Beman Dawes

Don't Miss BoostCon 2007! ==> http://www.boostcon.com