RE: [boost] Re: Runtime error reporting

From: Aleksey Gurtovoy (alexy_at_[hidden])
Date: 2001-03-20 16:30:15

 David Abrahams wrote:
> Actually, I disagree. IMO, the stuff in assert() is very easy 
> to separate from the mainline code. Everyone must follow the rule 
> "no side-effects in assert" anyway. Adding a VERIFY() macro just 
> gives us another macro to keep track of. How does it help in any 
> substantive way?

Taking Win32 API as an example, in theory almost every function call there
can fail, and consistent checking for it really helps to detect induced
errors (and their sources, of course). The problem with having only classic
'assert'-like macro as a checking tool for such errors is that consistent
application of "check a return value of every API function call" policy
makes your code much more bloated and clumsy, e.g.:

void clipboard::put_text(std::string const& text) {
  HGLOBAL handle = ::GlobalAlloc( GHND, text.length() + 1 );
  // copy text to allocated memory
  // ..
  // copy text to clipboard
  bool result1 = ::OpenClipboard(0);
  assert(result1);
  bool result2 = ::EmptyClipboard();
  assert(result2);
  bool result3 = ::SetClipboardData(CF_TEXT, handle);
  assert(result3);
  bool result4 = ::CloseClipboard();
  assert(result4);
}

vs.

void clipboard::put_text(std::string const& text) {
  HGLOBAL handle = ::GlobalAlloc( GHND, text.length() + 1 );
  // copy text to allocated memory
  // ..
  // copy text to clipboard
  sys_verify(::OpenClipboard(0));
  sys_verify(::EmptyClipboard());
  sys_verify(::SetClipboardData(CF_TEXT, handle));
  sys_verify(::CloseClipboard());
}

You can beautify the first version a little by rearranging the code like
this:

  { bool result = ::OpenClipboard(0); assert(result); }
  { bool result = ::EmptyClipboard(); assert(result); }
  // etc.

but IMO 'sys_verify' version is still much more appealing here.

Aleksey