Open MPI "Hello, World!" is not compiling
c++, g++, mpi
Solution
Just place the mpi.h header file above all header files sometimes that causes problem to compile
I am not sure how u execute your code. Compiling
mpic++ your_code_file.c
Execution
mpirun -np <no. of Processors> ./a.out
Problem
Here is a simple MPI "Hello, World!" program. ``` #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); } ``` However, it doesn't seem to compile: ``` Undefined first referenced symbol in file MPI::Datatype::Free() /var/tmp//ccE6aG2w.o MPI::Win::Free() /var/tmp//ccE6aG2w.o MPI::Comm::Comm() /var/tmp//ccE6aG2w.o ld: fatal: symbol referencing errors. No output written to main collect2: ld returned 1 exit status ``` I've googled a lot, viewed mailing lists, thousands of them. They say `libmpi_cxx` is not linking. But it's in the compiler flags. Here is `--showme` data: ``` mpic++ --showme:compile -I/usr/openmpi/ompi-1.5/include -I/usr/openmpi/ompi-1.5/include/openmpi mpic++ --showme:link -R/opt/mx/lib -R/usr/openmpi/ompi-1.5/lib -L/usr/openmpi/ompi-1.5/lib -lmpi -lopen-rte -lopen-pal -lnsl -lrt -lm -ldl -lsocket -lmpi_cxx ``` My compiler is g++.