mpicc(1)                           Open MPI                           mpicc(1)



NAME
       mpicc -- Open MPI C wrapper compiler

SYNTAX
       mpicc [-showme|-showme:compile|-showme:link] ...

OPTIONS
       -showme
              Do not invoke the underlying compiler.  Instead, show 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
              Do not invoke the underlying C compiler.  Instead, show the
              compiler flags that would be supplied to the C compiler.

       -showme:link
              Do not invoke the underlying C compiler.  Instead, show the
              linker flags that would be supplied to the C compiler.

       See the man page for your underlying 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



1.4.1                            Jan 14, 2010                         mpicc(1)
