According to http://gcc.gnu.org/onlinedocs/cpp/If.html
"The `#if' directive allows you to test the value of an arithmetic expression, rather than the mere existence of one macro." Is the objective to test for the existence of the macro, its value, or its value IFF it exists? Ken Lloyd -----Original Message----- From: devel-boun...@open-mpi.org [mailto:devel-boun...@open-mpi.org] On Behalf Of Jeff Squyres Sent: Monday, September 12, 2011 7:07 AM To: Open MPI Developers Subject: Re: [OMPI devel] RFC: make hwloc be a 1st-class citizen On Sep 12, 2011, at 8:51 AM, Jeff Squyres wrote: > *** Remember that although the opal_hwloc_topology global variable will always be available, ##IT MAY BE NULL## on platforms where hwloc was compiled out / not supported. Therefore, you MUST protect access to hwloc API calls with #if OPAL_HAVE_HWLOC! See the original RFC text below. Oops! Ralph just reminded me that this was slightly inaccurate. If hwloc is not present, then the global variable opal_hwloc_topology won't be present at all (because its corresponding hwloc type won't be available). Hence, the example in the original RFC isn't quite right: >> if (NULL != opal_hwloc_topology) { >> #if OPAL_HAVE_HWLOC >> // ...use hwloc API, etc. >> #endif >> } This really should be: #if OPAL_HAVE_HWLOC if (NULL != opal_hwloc_topology) { // ...use hwloc API, etc. } #endif Sorry for the confusion! -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/ _______________________________________________ devel mailing list de...@open-mpi.org http://www.open-mpi.org/mailman/listinfo.cgi/devel ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1392 / Virus Database: 1520/3891 - Release Date: 09/11/11
