mpi comm 划分

Maybe it can‘t be run ，but it just provides a thinking way and mpi api overview.

#include "mpi.h"
#include <stdio.h>
#include <unistd.h>
#define nodeNameLength 20

int main(int argc, char  *argv[])
{
    int rank,nproc;   
    MPI_Init( &argc, &argv );
    MPI_Comm_size( MPI_COMM_WORLD, &nproc);
    MPI_Comm_rank( MPI_COMM_WORLD, &rank);


    char currentNodeName[nodeNameLength];  

    if(-1==gethostname(currentNodeName,sizeof(currentNodeName)))
        {
            perror("gethostname error !");
            return;
        }
    char numStr[nodeNameLength];
    int i=-1;//************************just a count variable
    for(i=4;i<strlen(currentNodeName);i++)
        {numStr[i]=currentNodeName[i];//numStr is a string which only includes number
        }
    numStr[i]='\0';

    int num =atoi(numStr);//convert string to number

    int allName[nproc];

    //root process get information of nodes.    
    MPI_Gather(&num, 1, MPI_BYTE, allName, nproc, MPI_BYTE, 0,MPI_COMM_WORLD);

    int rankofnode[nproc];  

    if(0==rank)
        {for(i=0;i<nproc;i++)
             {              
                int noderank=0;             
                int j=-1;
                for(j=0;j<=i;j++)
                    {
                     if(allName[i]==allName[j])
                        noderank++;
                    }
                rankofnode[i]=noderank;
             }

        }   
    MPI_Bcast(rankofnode,,MPI_BYTE,0,MPI_COMM_WORLD);

    MPI_Comm myWorld,nodeWorld;
    MPI_Comm_dup(MPI_COMM_WORLD,&myWorld);
    MPI_Common_split(myWorld,num,rankofnode[rank],&nodeWorld);

    int members[nproc];
    int head_num=0;
    for(i=0;i<nproc;i++)
        {if(0==rankofnode[i])
            {
            members[head_num]=i;//members store the set of head member
            head_num++;
            }
        }

    MPI_Group group_world,head_group;
    MPI_Comm head_comm;
    MPI_COMM_group(MPI_COMM_WORLD,&group_world);
    MPI_Group_incl(group_world,head_num,members,&head_group);
    MPI_Comm_create(MPI_COMM_WORLD,head_group,&head_comm);


    //At now ,The node communication and head head communication are created.








    MPI_Finalize();
    return 0;
}