.TH mpicc 1 "Open MPI" "OMPI" "Open MPI"..SH NAMEmpicc -- Open MPI C wrapper compiler..SH SYNTAXmpicc [-showme|-showme:compile|-showme:link] .....SH OPTIONS.TP-showme Do not invoke the underlying compiler.  Instead, show the command linethat would be executed to compile the program.  \fBNOTE:\fR If anon-filename argument is passed on the command line, the \fI-showme\fRoption will \fInot\fR display any additional flags.  For example, both"mpicc --showme" and "mpicc --showme my_source.c" will show all thewrapper-supplied flags.  But "mpicc -showme -v" will only show theunderlying compiler name and "-v"..TP-showme:compileDo not invoke the underlying C compiler.  Instead, show thecompiler flags that would be supplied to the C compiler..TP-showme:linkDo not invoke the underlying C compiler.  Instead, show the linkerflags that would be supplied to the C compiler..PPSee the man page for your underlying compiler for other options thatcan be passed through mpicc...SH DESCRIPTION.PPConceptually, the role of these commands is quite simple:transparently add relevant compiler and linker flags to the user'scommand line that are necessary to compile / link Open MPIprograms, and then invoke the underlying compiler to actually performthe command...PPAs such, these commands are frequently referred to as "wrapper"compilers because they do not actually compile or link applicationsthemselves; they only add in command line flags and invoke theback-end compiler....SS BackgroundOpen MPI is comprised of three software layers: OPAL (Open PortableAccess Layer), ORTE (Open Run-Time Environment), and OMPI (Open MPI).There are wrapper compilers for each layer; each layer's wrapper onlylinks in the libraries relevant for that layer.  Specifically, eachlayer provides the following wrapper compilers:..TP 4OPAL\fIopalcc\fR and \fIopalc++\fR..TPORTE\fIortecc\fR and \fIortec++\fR..TPOMPI\fImpicc\fR, \fImpic++\fR, \fImpicxx\fR, \fImpiCC\fR (only on systems withcase-senstive file systems), \fImpif77\fR, and \fImpif90\fR.  Notethat \fImpic++\fR, \fImpicxx\fR, and \fImpiCC\fR all invoke the sameunderlying C++ compiler with the same options.  All are provided ascompatibility with other MPI implementations...PPThe Fortran wrapper compilers for MPI (\fImpif77\fR and \fImpif90\fR)will be inoperative and will return an error on use if Fortran 77 /Fortran 90 support was not built into the MPI layer....SS Overview\fImpicc\fR is a convenience wrappers for the underlyingC compiler.  Translation of an Open MPI program requires thelinkage of the Open MPI-specific libraries which may not reside inone of the standard search directories of ld(1).  It also oftenrequires the inclusion of header files what may also not be found in astandard location...PP\fImpicc\fR passes its arguments to the underlying Ccompiler along with the -I, -L and -l options required by Open MPIprograms...PPThe Open MPI Team \fIstrongly\fR encourages using the wrappercompilers instead of attempting to link to the Open MPI librariesmanually.  This allows the specific implementation of Open MPI tochange without forcing changes to linker directives in users'Makefiles.  Indeed, the specific set of flags and libraries used bythe wrapper compilers depends on how Open MPI was configured andbuilt; the values can change between different installations of thesame version of Open MPI...PPIndeed, since the wrappers are simply thin shells on top of anunderlying compiler, there are very, very few compelling reasons\fInot\fR to use \fImpicc\fR.  When it is not possible to use thewrappers directly, the \fI-showme:compile\fR and \fI-showme:link\fRoptions should be used to determine what flags the wrappers would haveused.  For example:..PPshell$ cc -c file1.c `mpicc -showme:compile`..PPshell$ cc -c file2.c `mpicc -showme:compile`..PPshell$ cc file1.o file2.o `mpicc -showme:link` -o my_mpi_program...SH NOTES.PPIt is possible to make the wrapper compilers multi-lib aware.  Thatis, the libraries and includes specified may differ based on thecompiler flags specified (for example, with the GNU compilers onLinux, a different library path may be used if -m32 is seen versus-m64 being seen).  This is not the default behavior in a standardbuild, but can be activated (for example, in a binary packageproviding both 32 and 64 bit support).  More information can be foundat:.PP  https://svn.open-mpi.org/trac/ompi/wiki/compilerwrapper3264...SH FILES.PPThe string that the wrapper compilers insert into the command linebefore invoking the underlying compiler are stored in a text filecreated by Open MPI and installed to\fI$pkgdata/mpicc-wrapper-data.txt\fR, where \fI$pkgdata\fRis typically \fI$prefix/share/openmpi\fR, and \fI$prefix\fR is the topinstallation directory of Open MPI...PPIt is rarely necessary to edit this file, but it can be examined togain insight into what flags the wrappers are placing on the commandline....SH ENVIRONMENT VARIABLES.PP By default, the wrappers use the compilers that were selected whenOpen MPI was configured.  These compilers were either foundautomatically by Open MPI's "configure" script, or were selected bythe user in the CC, CXX, F77, and/or FC environment variables before "configure" was invoked.  Additionally, other argumentsspecific to the compiler may have been selected by configure...PPThese values can be selectively overridden by either editing the textfiles containing this configuration information (see the \fBFILES\fRsection), or by setting selected environment variables of theform "OMPI_value"...PPValid value names are:..TPCPPFLAGSFlags added when invoking the preprocessor (C or C++)..TPLDFLAGSFlags added when invoking the linker (C, C++, or Fortran)..TPLIBSLibraries added when invoking the linker (C, C++, or Fortran)..TPCCC compiler..TPCFLAGSC compiler flags..TPCXXC++ compiler..TPCXXFLAGSC++ compiler flags...TPF77Fortran 77 compiler..TPFFLAGSFortran 77 compiler flags...TPFCFortran 90 compiler..TPFCFLAGSFortran 90 compiler flags