[mpich-discuss] Nifty workaround for SEEK_SET issues

[Jeff Squyres]

Per our discussion in Dublin, here's a nifty solution for the  
MPI::SEEK_SET issue that was proposed Doug Gregor from Indiana:

mpicxx.h:
#include <stdio.h>
const int your_mpi_stdio_seek_set = (SEEK_SET);
#undef SEEK_SET
const int SEEK_SET = your_mpi_stdio_seek_set;

(and the same for the others)

Since the stdio_seek_set variable is const, this is basically an end- 
run around the preprocessor but the compiler will still treat it like  
a *constant* (it will likely not even generate a symbol for it).  Doug  
felt that every compiler would get this right, but we put a "static"  
on those two declarations, just to be sure.

Note that we found that we also need to #include <iostream> after  
<stdio.h> but before smashing SEEK_SET for obscure reasons on Linux  
(using SEEK_SET as an enum value), so you need to force its inclusion  
early.  A bummer, but it's an imperfect world...

Note that Solaris 10u6 just introduced a new #define named LOCK_SHARED  
from <sys/asynch.h>) that conflicts with MPI::LOCK_SHARED.  A similar  
approach can be used there.  The logic gets a little more complex  
because you need to conditionally include <sys/asynch.h> (which seems  
to only exist on Solaris) so that you can smash the LOCK_SHARED macro.

-- 
Jeff Squyres
Cisco Systems