NAME

       mpicc -- Open MPI C wrapper compiler

SYNTAX

       mpicc [-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  "mpicc  --showme"  and
              "mpicc  --showme my_source.c" will show all the wrapper-supplied flags.  But "mpicc
              --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.

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

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),
           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.

       The Fortran wrapper compilers for MPI (mpif77 and mpif90) will  be  inoperative  and  will
       return  an  error  on  use  if  Fortran 77 / Fortran 90 support was not built into the MPI
       layer.

   Overview
       mpicc 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.

       mpicc  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 mpicc.  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://svn.open-mpi.org/trac/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/mpicc-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

       F77    Fortran 77 compiler

       FFLAGS Fortran 77 compiler flags

       FC     Fortran 90 compiler

       FCFLAGS
              Fortran 90 compiler flags