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SYNTAX
mpicc [--showme | --showme:compile | --showme:link] ...
mpic++ [--showme | --showme:compile | --showme:link] ...
mpicxx [--showme | --showme:compile | --showme:link] ...
mpifort [--showme | --showme:compile | --showme:link] ...
mpijavac [--showme | --showme:compile | --showme:link] ...
The following deprecated commands are also available — but mpifort should be used instead:
mpif77 [--showme | --showme:compile | --showme:link] ...
mpif90 [--showme | --showme:compile | --showme:link] ...
On case-sensitive filesystems, the following command will also be available:
mpiCC [--showme | --showme:compile | --showme:link] ...
OPTIONS
The options below apply to all of the wrapper compilers:
• --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 underlying compiler.
• --showme:link: Output the linker flags that would have been supplied to the underlying compiler.
• --showme:command: Outputs the underlying 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 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-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 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 provides wrapper compilers for several languages:
• mpicc: C
• mpic++, mpicxx (and on systems with case-sensitive file systems, mpiCC): C++
NOTE:
mpic++, mpicxx, and mpiCC all invoke the same underlying C++ compiler with the same options. All are
provided as compatibility with other MPI implementations.
• mpifort (and its legacy/deprecated aliaes mpif77 and mpif90): Fortran
• mpijavac: Java
The wrapper compilers for each of the languages are identical; they can be use interchangeably. The
different names are provided solely for backwards compatibility.
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 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 same is true for all the other language wrapper compilers.
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 Open MPI’s wrapper compilers. 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 here.
FILES
The strings 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/NAME-wrapper-data.txt,
where:
• $pkgdata is typically $prefix/share/openmpi
• $prefix is the top installation directory of Open MPI
• NAME is the name of the wrapper compiler (e.g., $pkgdata/mpicc-wrapper-data.txt)
It is rarely necessary to edit these files, but they 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, 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
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Feb 17, 2025 OMPI-WRAPPER-COMPILER(1)