File IO
C | Fortran-2008 | Fortran-90
MPI_MODE_RDONLY is a flag that can be passed to MPI_File_open to ask for read-only access to the file. It cannot be used in conjunction with MPI_MODE_WRONLY or MPI_MODE_RDWR. Also, MPI_MODE_RDONLY cannot be used in conjunction with MPI_MODE_CREATE or MPI_MODE_EXCL.
Other flags are MPI_MODE_RDWR, MPI_MODE_WRONLY, MPI_MODE_CREATE, MPI_MODE_EXCL, MPI_MODE_DELETE_ON_CLOSE, MPI_MODE_UNIQUE_OPEN, MPI_MODE_SEQUENTIAL and MPI_MODE_APPEND.
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
/**
* @brief Illustrates how to specify that a file must be open in read-only mode.
* @details Since MPI_MODE_RDONLY is incompatible with MPI_MODE_CREATE and
* MPI_MODE_EXCL, the file to open must be existing already. Therefore, this
* application contains a preparatory phase where the MPI process 0 creates an
* empty file so that the file exists by the time the MPI_File_open is issued.
**/
int main(int argc, char* argv[])
{
MPI_Init(&argc, &argv);
int my_rank;
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
// PREPARATORY PHASE: MPI process 0 creates the file
if(my_rank == 0)
{
// If the file does not exist, it will be created automatically
FILE* tmp_file = fopen("file.tmp", "w");
if(!tmp_file)
{
printf("[MPI process 0] Cannot create the file 'file.tmp'.\n");
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
fclose(tmp_file);
}
MPI_Barrier(MPI_COMM_WORLD);
// END OF PREPARATORY PHASE
MPI_File handle;
int access_mode = MPI_MODE_RDONLY; /* With read-only access */
if(MPI_File_open(MPI_COMM_WORLD, "file.tmp", access_mode, MPI_INFO_NULL, &handle) != MPI_SUCCESS)
{
printf("[MPI process %d] Failure in opening the file.\n", my_rank);
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
printf("[MPI process %d] File opened successfully.\n", my_rank);
if(MPI_File_close(&handle) != MPI_SUCCESS)
{
printf("[MPI process %d] Failure in closing the file.\n", my_rank);
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
printf("[MPI process %d] File closed successfully.\n", my_rank);
MPI_Finalize();
return EXIT_SUCCESS;
}