NAME

       mpicxx -- Open MPI C++ wrapper compiler

SYNTAX

       mpicxx [-showme|-showme:compile|-showme:link] ...

OPTIONS

       --showme
              This  option comes in several different variants (see below).  None of the variants
              invokes the underlying compiler; they all provide information on how the underlying
              compiler  would  have  been invoked had --showme not been used.  The basic --showme
              option outputs the command line that would be  executed  to  compile  the  program.
              NOTE:  If a non-filename argument is passed on the command line, the -showme option
              will not display any additional flags.  For example,  both  "mpicxx  --showme"  and
              "mpicxx  --showme  my_source.c"  will  show  all  the  wrapper-supplied flags.  But
              "mpicxx --showme -v" will only show the underlying compiler name and "-v".

       --showme:compile
              Output the compiler flags that would have been supplied to the C++ compiler.

       --showme:link
              Output the linker flags that would have been supplied to the C++ compiler.

       --showme:command
              Outputs the underlying C++ compiler command (which may be one or more tokens).

       --showme:incdirs
              Outputs a space-delimited (but otherwise undecorated) list of directories that  the
              wrapper  compiler  would  have  provided to the underlying C++ compiler to indicate
              where relevant header files are located.

       --showme:libdirs
              Outputs a space-delimited (but otherwise undecorated) list of directories that  the
              wrapper  compiler  would  have  provided to the underlying linker to indicate where
              relevant libraries are located.

       --showme:libs
              Outputs a space-delimited (but otherwise undecorated) list of  library  names  that
              the  wrapper  compiler  would  have used to link an application.  For example: "mpi
              open-rte open-pal util".

       --showme:version
              Outputs the version number of Open MPI.

       --showme:help
              Output a brief usage help message.

       See the man page for your underlying C++ compiler for other options  that  can  be  passed
       through mpicxx.

DESCRIPTION

       Conceptually,  the  role  of  these  commands  is quite simple: transparently add relevant
       compiler and linker flags to the user's command line that are necessary to compile /  link
       Open  MPI  programs,  and  then  invoke  the  underlying  compiler to actually perform the
       command.

       As such, these commands are frequently referred to as "wrapper" compilers because they  do
       not  actually compile or link applications themselves; they only add in command line flags
       and invoke the back-end compiler.

   Background
       Open MPI is comprised of three software layers: OPAL (Open Portable  Access  Layer),  ORTE
       (Open  Run-Time  Environment),  and OMPI (Open MPI).  There are wrapper compilers for each
       layer; each layer's  wrapper  only  links  in  the  libraries  relevant  for  that  layer.
       Specifically, each layer provides the following wrapper compilers:

       OPAL
           opalcc and opalc++

       ORTE
           ortecc and ortec++

       OMPI
           mpicc,  mpic++,  mpicxx,  mpiCC (only on systems with case-senstive file systems), and
           mpifort (and its legacy/deprecated  names  mpif77  and  mpif90).   Note  that  mpic++,
           mpicxx,  and  mpiCC all invoke the same underlying C++ compiler with the same options.
           All are provided as compatibility with other MPI implementations.

   Fortran Notes
       The Fortran wrapper compiler for MPI (mpifort, and its legacy/deprecated names mpif77  and
       mpif90)  can  compile  and  link  MPI  applications  that  use  any/all of the MPI Fortran
       bindings: mpif.h, the mpi module, and the mpi_f08 module (assuming Open MPI was  installed
       with support for each of these Fortran bindings).  Specifically: it is no longer necessary
       to use different wrapper compilers for applications that use mpif.h vs. applications  that
       use the mpi module -- just use mpifort for all Fortran MPI applications.

       Note,  however,  that  the Fortran compiler may require additional command-line options to
       enforce a specific Fortran dialect.   For  example,  in  some  versions  of  the  IBM  XLF
       compiler, if xlf90 is the underlying Fortran compiler, -qfixed may be necessary to compile
       fixed-format Fortran source files.

       Finally, note that mpifort will be inoperative and will return an error on use if  Fortran
       support was not built into the MP Ilayer.

   Overview
       mpicxx  is a convenience wrappers for the underlying C++ compiler.  Translation of an Open
       MPI program requires the linkage of the Open MPI-specific libraries which may  not  reside
       in  one of the standard search directories of ld(1).  It also often requires the inclusion
       of header files what may also not be found in a standard location.

       mpicxx passes its arguments to the underlying C++ compiler along with the -I,  -L  and  -l
       options required by Open MPI programs.

       The Open MPI Team strongly encourages using the wrapper compilers instead of attempting to
       link to the Open MPI libraries manually.  This allows the specific implementation of  Open
       MPI  to  change without forcing changes to linker directives in users' Makefiles.  Indeed,
       the specific set of flags and libraries used by the wrapper compilers depends on how  Open
       MPI was configured and built; the values can change between different installations of the
       same version of Open MPI.

       Indeed, since the wrappers are simply thin shells on top of an underlying compiler,  there
       are  very,  very few compelling reasons not to use mpicxx.  When it is not possible to use
       the wrappers directly, the -showme:compile and -showme:link  options  should  be  used  to
       determine what flags the wrappers would have used.  For example:

       shell$ cc -c file1.c `mpicc -showme:compile`

       shell$ cc -c file2.c `mpicc -showme:compile`

       shell$ cc file1.o file2.o `mpicc -showme:link` -o my_mpi_program

NOTES

       It  is possible to make the wrapper compilers multi-lib aware.  That is, the libraries and
       includes specified may differ based on the compiler flags specified (for example, with the
       GNU  compilers  on Linux, a different library path may be used if -m32 is seen versus -m64
       being seen).  This is not the default behavior in a standard build, but can  be  activated
       (for example, in a binary package providing both 32 and 64 bit support).  More information
       can be found at:

         https://github.com/open-mpi/ompi/wiki/compilerwrapper3264

FILES

       The string that the wrapper compilers insert into the command  line  before  invoking  the
       underlying  compiler  are  stored  in  a  text  file  created by Open MPI and installed to
       $pkgdata/mpicxx-wrapper-data.txt, where $pkgdata is typically  $prefix/share/openmpi,  and
       $prefix is the top installation directory of Open MPI.

       It is rarely necessary to edit this file, but it can be examined to gain insight into what
       flags the wrappers are placing on the command line.

ENVIRONMENT VARIABLES

       By default, the  wrappers  use  the  compilers  that  were  selected  when  Open  MPI  was
       configured.   These  compilers  were  either found automatically by Open MPI's "configure"
       script, or were selected by the user in the CC, CXX, F77, and/or FC environment  variables
       before  "configure"  was  invoked.  Additionally, other arguments specific to the compiler
       may have been selected by configure.

       These values can be selectively overridden by either editing  the  text  files  containing
       this configuration information (see the FILES section), or by setting selected environment
       variables of the form "OMPI_value".

       Valid value names are:

       CPPFLAGS
              Flags added when invoking the preprocessor (C or C++)

       LDFLAGS
              Flags added when invoking the linker (C, C++, or Fortran)

       LIBS   Libraries added when invoking the linker (C, C++, or Fortran)

       CC     C compiler

       CFLAGS C compiler flags

       CXX    C++ compiler

       CXXFLAGS
              C++ compiler flags

       FC     Fortran compiler

       FCFLAGS
              Fortran compiler flags