Re: Use of config.h: summary of responses.

[Bob Friesenhahn]

On Mon, 13 Sep 2004, Daniel Reed wrote:
> Ideally, interface files will conform to some specific environment, have
> that environment documented, and rely on dependent projects to use something
> like the autotools to ensure their build environment conforms.
>
> Changes to the compiler, CPU, or OS should not cause interface files to
> change. The interface files should assume reasonable details about the
> environment.
>
> With that said, can you provide an example of an OS-, CPU-, or compiler-
> dependent attribute that must be recorded in installed interface files to
> ensure ABI and unambiguous API?

  1) Large file interface (off_t,fpos_t,rlim_t, etc., size changes).
  2) 'const' support
  3) 'inline' support
  4) Big/little endian CPU type.
  5) User supplied configuration options which influence available
     interfaces.

> gnu89 and C99 provide guarantees about types and non-C89 routines that can
> be documented and simulated by the autotools.

Autoconf is not about guarantees.  It is all about survival without 
guarantees.

> POSIX and various other environment standards provide guarantees about
> networking, file system interaction, and other low-level operations that can
> be simulated by support libraries, as with the Cygwin kernel or Solaris'
> libnsl.

Everything would be easier if we all used operating systems designed 
to the exact same standards and which provided the exact same APIs. 
Unfortunately, this will never happen.  Standards have created a 
kinder and gentler world, but there will always be variances.  In many 
cases we must compile on systems which are frozen in time so they 
conform to very old standards (if at all).

> The availability of extension libraries can be hidden through the API
> itself, and good software design can make it possible for extension

I agree that good design and forethought can go a long way at reducing 
chaos.

Notice that I mention LF issues as the first item.  Libraries which 
expose types which are influenced by large-file compilation do not 
illustrate good design and forethought.

Bob
======================================
Bob Friesenhahn
address@hidden
http://www.simplesystems.org/users/bfriesen