MPI_Send和MPI_Recv

Question

为什么这些代码行：

if(my_rank != 0) {
    sprintf(msg, "Hello from %d of %d...", my_rank, comm_sz);
    if(my_rank == 2) {
        sleep(2);
        sprintf(msg, "Hello from %d of %d, I have slept 2 seconds...", my_rank, comm_sz);
    }
    MPI_Send(msg, strlen(msg), MPI_CHAR, 0, 0, MPI_COMM_WORLD);
}
else {
    printf("Hello from the chosen Master %d\n", my_rank);
    for(i = 1; i < comm_sz; i++) {
        MPI_Recv(msg, MAX_STRING, MPI_CHAR, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
        printf("%s\n", msg);
    }
}

给出这个结果？

Hello from the chosen Master 0  
Hello from 1 of 5...  
Hello from 2 of 5, I have slept 2 seconds...  
Hello from 3 of 5... have slept 2 seconds...  
Hello from 4 of 5... have slept 2 seconds...

每个进程都不具有'msg'的副本吗？

Answer 1

strlen()不包含空终止符，因此不会将其发送给主节点。从秩3接收消息不会覆盖字符串的后半部分，因此仍会显示。您应该使用strlen(msg) + 1作为发送计数。