(3) MPI-IO: MPI_File_read_at_all MPI_File_read_at_all

#include<stdio.h>#include<stdlib.h>#include<string.h>#include"mpi.h"/** * all process read/write at the same offset * int MPI_File_read_at_all(MPI_File fh, MPI_Offset offset, void *buf, int count, MPI_Datatype datatype, MPI_Status * status) * int MPI_File_read_at_all(MPI_File fh, MPI_Offset offset, void *buf, int count, MPI_Datatype datatype, MPI_Status * status) */int main(int argc, char *argv[]){int totalTaskNum, rankID;MPI_Init(&argc, &argv);MPI_Comm_rank(MPI_COMM_WORLD, &rankID);MPI_Comm_size(MPI_COMM_WORLD, &totalTaskNum);char *filename = "file.txt";MPI_File fh;MPI_Status status;MPI_File_open(MPI_COMM_WORLD, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);MPI_Offset offset = 0;char buf[100];strcpy(buf, "hello, world!");//strlen(buf) = 13 while sizeof(buf) = 100MPI_File_write_at_all(fh, offset, buf, strlen(buf), MPI_CHAR, &status);MPI_File_read_at_all(fh, offset, buf, sizeof(buf), MPI_CHAR, &status);printf("rankID = %d, buf = %s\n", rankID, buf);MPI_File_close(&fh);//after open, fh has the communicator infoMPI_Finalize();return 0;}