Re: Precompiled headers hiding bad c++

Hi folks,

I've got a multi-platform C++ application that I'm working on, and
found some behavior associated with pre-compiled headers that I find
confusing.

I built and tested my code on a windows box, using VC++ 2003 (version
7.1.3088) (BTW, for the next release we're planning on upgrading to
2008). Everything worked great. When I moved that same code to the
mac, I got a bunch of compilation errors.

What I found was that somehow I fat-fingered one of my .cpp files,
such that the first character was a '7'. The file looked something
like this:

7/*+
+**************************************************************************
** FileCacheTest.cpp
**************************************************************************--
*/
#include "stdafx.h"
#include "AsOfDate.h"
#include "FileCache.h"

This compiled just fine on Windows, and obviously its bad C++ code.
For yahoos, we started typing in all sorts of garbage to see where we
could get it to actually give an error. When we got to this code:

7hafuhweifhweuhfalseeiwtfjiohwoiefj/*+
+**************************************************************************
** FileCacheTest.cpp
**************************************************************************--
*/
#include "stdafx.h"
#include "AsOfDate.h"
#include "FileCache.h"

we were getting very puzzled.

One of my co-workers suggested turning off "use precomipled headers"
for this file, and all of a sudden we started getting a bunch of
compile errors.

So, the question I have is: why? What is it about using precompiled
headers which caused this obvious problem in a c++ file to get past
the compiler?