[OMPI users] Problem with MPI functions

[Ng Shi Wei]

Dear all,
I am new in OpenMPI and writing a parallel processing program using openmpi in 
C++ language. I would like to use the function MPI_Allreduce() but my sendbuf 
and recvbuf datatype are pointers/arrays (2D). 
Is it possible to pass in and out the pointers/arrays using the MPI_Allreduce() 
?
If yes, hope can have some guidelines provided on how to write the command.
Thanks in advance.
Best Regards,Shi Wei