(7) MPI-IO: MPI_File_seek

fileview + seek  能组合出非常强大的功能，首先由fileview来抽象进程自己的文件视图，然后再在新的fileview逻辑视图中seek想要达到的位置。而不关心物理位置。

#include<stdio.h>#include<stdlib.h>#include<string.h>#include"mpi.h"/** * int MPI_File_seek(MPI_File fh, MPI_Offset offset, int whence) * here whence can be: *MPI_SEEK_SET, point to offset *MPI_SEEK_CUR, point to current+offset *MPI_SEEK_END, point to end+offset *according to fh *if fh is refreshed by setting fileview, then the seek operation is under the context of new fileview *otherwise, seek is under the original fileview */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 = rankID * 128;//each process will has its file view which starts with offsetMPI_File_set_view(fh, offset, MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL);MPI_Offset seek_offset = 2;int whence = MPI_SEEK_SET;//after set fileview, the seek is the context of new fileviewMPI_File_seek(fh, seek_offset, whence);char read_buf[128];MPI_File_read(fh, read_buf, sizeof(read_buf), MPI_CHAR, &status);printf("rankID = %d, content = \'%s\'\n", rankID, read_buf);MPI_File_close(&fh);//after open, fh has the communicator infoMPI_Finalize();return 0;}