Hello,
I have a MPI/C++ code for parallel reading from a single data file. There seems
to be some problem which I am not able to figure out. Pls point out my mistake.
Here is the code, data file and input:
// example of parallel MPI read from single file, in C++
#include <iostream.h>
#include <mpi.h>
int main(int argc, char **argv)
{
int bufsize, buf[15], count,rank,nprocs,i;
MPI_File fh;
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
bufsize = sizeof(int)*30 / nprocs ; // local number to read
nints = bufsize/sizeof (int);
MPI_File_open
(MPI_COMM_WORLD,"testfile.dat",MPI_MODE_RDONLY,MPI_INFO_NULL,&fh);
MPI_File_seek(fh,rank*bufsize,MPI_SEEK_SET);
MPI_File_read(fh,&buf,nints,MPI_INT,&status);
MPI_File_close(&fh);
if(rank == 0) for(i=0;i<15;i++) cout<<"rank = "<<rank<<" "<<" i
= "<<i<<" "<<buf[i]<<endl;
free (buf);
MPI_Finalize();
return 0;
}
DATA FILE:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
OUTPUT:
mpirun -np 1 MPIfilehandling testfile.dat
rank = 0 i = 0 822751754
rank = 0 i = 1 856306698
rank = 0 i = 2 889861642
rank = 0 i = 3 923416586
rank = 0 i = 4 956969264
rank = 0 i = 5 170995978
rank = 0 i = 6 825362993
rank = 0 i = 7 856305972
rank = 0 i = 8 170997002
rank = 0 i = 9 825625137
rank = 0 i = 10 923414840
rank = 0 i = 11 170998026
rank = 0 i = 12 842009138
rank = 0 i = 13 822751794
rank = 0 i = 14 171062026
Why buf[i] is not reading the desired data. Pls suggest.
Thanks,
--
Ravi R. Kumar
859-333-8174
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