mpic++(1) Open MPI mpic++(1)NAME
mpic++ -- Open MPI C++ wrapper compiler
SYNTAX
mpic++ [-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 com‐
pile the program. NOTE: If a non-filename argument is passed on
the command line, the -showme option will not display any addi‐
tional flags. For example, both "mpic++ --showme" and "mpic++
--showme my_source.c" will show all the wrapper-supplied flags.
But "mpic++ --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 mpic++.
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" compil‐
ers because they do not actually compile or link applications them‐
selves; 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 imple‐
mentations.
The Fortran wrapper compilers for MPI (mpif77 and mpif90) will be inop‐
erative and will return an error on use if Fortran 77 / Fortran 90 sup‐
port was not built into the MPI layer.
Overview
mpic++ 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.
mpic++ 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 forc‐
ing changes to linker directives in users' Makefiles. Indeed, the spe‐
cific 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 underly‐
ing compiler, there are very, very few compelling reasons not to use
mpic++. 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 dif‐
ferent 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 cre‐
ated by Open MPI and installed to $pkgdata/mpic++-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 sec‐
tion), 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
1.6.4 Feb 19, 2013 mpic++(1)
