Provided by: openmpi-bin_4.1.6-7ubuntu2_amd64 bug

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.

       --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 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), 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
       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://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/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

       FC     Fortran compiler

       FCFLAGS
              Fortran compiler flags

4.1.6                                             Sep 30, 2023                                          mpicc(1)