# mpicxx

Compiles and links MPI programs written in C++

## Description

This command can be used to compile and link MPI programs written in C++. It provides the options and any special libraries that are needed to compile and link MPI programs.

It is important to use this command, particularly when linking programs, as it provides the necessary libraries.

## Command line arguments

-show
  Show the commands that would be used without runnning them
-help
  Give short help
-cxx=name
  Use compiler `name` instead of the default choice. Use this only if the compiler is compatible with the MPICH library (see below)
-config=name
  Load a configuration file for a particular compiler. This allows a single `mpicxx` command to be used with multiple compilers.
-compile_info
  Show the steps for compiling a program. This option can be used to see what options and include paths are used by mpicxx.
-link_info
  Show the steps for linking a program. This optoin can be used to see what options and libraries are used by mpicxx.
-profile=name
  Use the MPI profiling given by name. See below for details
-mpe=name
  Use an MPE profiling library. The behavior is similar to using `-profile=mpe_name.conf`.
-echo
  Show exactly what this program is doing. This option should normally not be used.
others
  are passed to the compiler or linker. For example, `-c` causes files to be compiled, `-g` selects compilation with debugging on most systems, and `-o name` causes linking with the output executable given the name `name`.

## Environment Variables

The environment variables `MPICH_CXX` may be used to select different C++ compiler and linker. Note that since MPICH is built with a particular C and Fortran compiler, changing the compilers used can cause problems. Use this only if you could intermix code compiled with the different compilers.

The environment variable `MPICC_PROFILE` specifies a profile library and has the same effect as if `-profile=$MPICC_PROFILE` were used as an argument to `mpicc`. See the discussion of `-profile` below for more details.

## Compatible Compilers

The MPI library may be used with any compiler that uses the same lengths for basic data objects (such as `long double`) and that uses compatible run-time libraries. On many systems, the various compilers are compatible and may be used interchangably. There are exceptions; if you use the `MPICH_CXX` environment variable or the `-cxx=name` command-line argument to override the choice of compiler and encounter problems, try reconfiguring MPICH2 with the new compiler, and installing MPICH2 in a separate location. See the installation manual for more details.

## Examples

To compile a single file `foo.c`, use

       mpicxx -c foo.cxx

To link the output and make an executable, use

       mpicxx -o foo foo.o

Combining compilation and linking in a single command

       mpicxx -o foo foo.cxx

is a convenient way to build simple programs.

## Selecting a Profiling Library

The `-profile=name` argument allows you to specify an MPI profiling library to be used. `name` can have two forms:

A library in the same directory as the MPI library
The name of a profile configuration file

If `name` is a library, then this library is included before the MPI library. This allows the simple use of libraries that make use of the MPI profiling interface and that are installed in the same directory as the MPI library.

If `name.conf` is the name of a file in the sysconfdir directory, then this is read and may define the following variables:

PROFILE_PRELIB
  Libraries (and paths) to include before the MPI library
PROFILE_POSTLIB
  Libraries to include after the MPI library
PROFILE_INCPATHS
  C preprocessor arguments for any include files For example, to add `/usr/local/myprof/include` to the include path and the library `libmyprof.a` in `/usr/local/myprof/lib` to the link step, you could create the file `myprof.conf` with the lines

        PROFILE_PRELIB="-L/usr/local/myprof/lib -lmyprof"
        PROFILE_INCPATHS="-I/usr/local/myprof/include"

and place it in the sysconfdir directory (this directory is set at configure time when MPICH is built). Then using the command-line argument `-profile=myprof` will cause these definitions to be added to the relevant compile commands.

## See Also

mpif77, mpicc, mpif90, mpiexec

Location:mpicxx.txt