point-to-point communication（点对点通信）

#include<stdio.h>
#include"mpi.h"
int main(int argc, char **argv){
    MPI_Comm comm = MPI_COMM_WORLD;
    int size ,rank;
    MPI_Status status;
    char str[100];
    MPI_Init(&argc,&argv);
    MPI_Comm_size(comm,&size);
    MPI_Comm_rank(comm,&rank);
    if(rank == 0){
        strcpy(str,"hello world");
        printf("Process 0 send [%s] to process 1.\n",str);
        MPI_Send(str,strlen(str)+1,MPI_CHAR,1,99,comm);
        //发送的地址，消息长度，消息数据类型，接收进程号，消息标志，通信域
    }
    else if (rank == 1){
        MPI_Recv(str,100,MPI_CHAR,0,99,comm,&status);
        //存储消息的地址，接收的数量，消息数据类型，发送进程号，消息标志，通信域，接收状态
        printf("Process 1 received message [%s] from Process 0.\n",str);
    }
    MPI_Finalize();
    return 0;
}