PR fortran/51727: make module files reproducible, question on C++ in gcc

[Joseph S. Myers]

On Sat, 13 Oct 2012, Diego Novillo wrote:

> On 2012-10-13 14:04 , Tobias Schlüter wrote:
> > On 2012-10-13 20:00, Diego Novillo wrote:
> > > On 2012-10-13 09:26 , Tobias Schlüter wrote:
> > > > first a question also to non-gfortraners: if I want to use std::map,
> > > > where do I "#include <map>"?  In system.h?
> > > 
> > > No.  Ada includes system.h in pure C code.  Why not include it exactly
> > > where you need it?
> > 
> > Ok, I was just wondering if there's a rule because a quick grep revealed
> > no non-header source file that includes system headers.
> 
> Joseph or others may have reason to create a system.hxx file or some such, but
> in principle I don't see why we shouldn't include std library headers as we
> need them.
> 
> Joseph?

The poisoning of various standard library functions that should not be 
used directly in GCC can be problematic if system headers, using those 
functions, are included after that poisoning.  Thus in general it's better 
for system header includes to go in system.h, before the poisoning.

In addition, where there is some autoconf configuration about whether to 
include a header, it's generally preferred to keep down the number of 
places with such a conditional on host features (encapsulating whatever 
features the header provides in some way so that other code can use them 
unconditionally).

-- 
Joseph S. Myers
joseph@codesourcery.com