Enabling OpenMPI on Linux - c++

Question

I'm trying to enable OpenMPI on Ubuntu using CodeBlocks. I have already downloaded it using:
sudo apt-get install -y  autotools-dev g++ build-essential
openmpi1.6-bin openmpi1.6-doc libopenmpi1.6-dev
Afterwards I tried to run the following code:
#include <stdio.h>
#include <mpi.h>
int main(int argc, char **argv)
{
int size, rank;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
printf("SIZE = %d RANK = %d\n",size,rank);
MPI_Finalize();
return(0);
}
But I got this error:
fatal error: mpi.h: No such file or directory
Then I changed the c++ compiler from g++ to mpicxx as it's recommended here: FAQ: Compiling MPI.
But when I try to run my code now, I get the following bunch of errors:
openmpi.cpp|| undefined reference to `MPI_Init'|
openmpi.cpp|| undefined reference to `ompi_mpi_comm_world'|
openmpi.cpp|| undefined reference to `MPI_Comm_size'|
openmpi.cpp|| undefined reference to `ompi_mpi_comm_world'|
openmpi.cpp|| undefined reference to `MPI_Comm_rank'|
openmpi.cpp|| undefined reference to `MPI_Finalize'|
[...]
I assume, I have to add the Path or link the library, but I'm not sure how to achieve this. I also don't know where OpenMPI has been installed on my machine.
I have downloaded the folder from the website, as well, if that can help.
Update
After adding mpicxx to the linker and -pthread -L/opt/openmpi/lib -lmpi_cxx -lmpi -ldl -lm -Wl,--export-dynamic -lrt -lnsl -lutil -lm -ldl as additional flags, I finally can compile the code.
But now I get another error:
[[INVALID],INVALID] ORTE_ERROR_LOG: A system-required executable either could not be found or was not executable by this user in file ess_singleton_module_c at line 231
[...]
Soory! You were supposed to get help about:
orte_init:startup:internal-failure
But I couldn't open the file:
/usr/share/openmpi/help-orte-runtime: No such file or directory.

Answer 1

Most MPI libraries come with special compiler wrappers, e.g.:
mpicc for the C compiler;
mpic++/mpiCC/mpicxx for the C++ compiler;
mpif77/mpif90/mpif95 for the Fortran compiler;
other distribution-specific wrappers, e.g. mpiicc for Intel MPI library with Intel C Compiler.
These wrappers provide all options that are needed by the compiler in order to find the include files and link the proper libraries.
Therefore you have to update your project settings and change both the compiler and the linker to mpicxx.
Another option would be to run the following command:
mpicxx -showme:link
It will give you a list of options that you should add to the linker flags in your project's settings in order to properly link the executable with Open MPI.