Re: Re:Re: [boost] [compatibility headers] fixes for Borland

From: John Maddock (john_at_[hidden])
Date: 2004-03-12 08:18:56

> >> Compatibility headers (in boost\compatibility\cpp_c_headers)
> >> don't compile with BCB 6.4.
>
> >I'm confused why you would be using those - Borland supplies the new
style
> >headers with everything in namespace std already doesn't it?
>
> Here's our problem,
>
> In the serialization library there are 14 files that use functions from
the
> std namespace.  In order to compile these under VC 6.0 ( and perhaps other
> platforms ) we specify:
>
> #include <boost/compatibility/cpp_c_headers/cstring> // memcpy
>
> This resolves the issue with vc 6.0 ( and who knows who else ? maybe
STLPort
> ? ).  Conformant compilers don't seem to be affected adversely by this.
The
> code itself uses a standard "std::memcpy" and everything is pretty clean.
>
> Now comes along Borland - the files ccp_c_headers won't compiler here.  So
> now we're in a quandary.
>
> a) Sprinkle #ifdef BORLAND in those 14 files
> b) Tweak cpp_c_headers files
> c) Or ? what?
>
> What is the least worst way to handle this?
>
> If I have to use a) what is the point of even having cpp_c_headers?

Here's the problem: those headers were only supplied as a workaround for
compilers that don't supply new style headers at all, they all use the
following workaround:

#include <string.h>

namespace std{ using ::memcpy; } //etc

However for conforming compilers this is defective for two reasons:

It needlessly introduces C functions into the global namespace (including
<cstring> should not do that).
It shouldn't compile at all: memcpy is already declared in std, the version
in the global namespace is an alias introduced with a using declaration,and
importing it back into std *should fail*.

Now the interesting thing is, I know of only two vendors who are shipping
std conforming C headers: Borland and Metrowerks.  Since you don't mention
the latter my guess is you're not testing with it ;-)

The normal workaround that Boost libs have been using is:

#include <cstring>
#include <boost/config.hpp>
#ifdef BOOST_NO_STDC_NAMESPACE
namespace std{ using ::memcpy; }
#endif

If you have a lot of files that need to do this, then the normal practice is
to create your own private config header that contains that code.

John.