First we will look at the calls that are used to create, open, and close files.

Create:

int ncmpi_create(MPI_Comm comm, const char *fname, int mode, MPI_Info info, int *id)

Open:

int ncmpi_open(MPI_Comm comm, const char *fname, int mode, MPI_Info info, int *id)

Both create and open are collective calls over the MPI communicator comm. The mode parameter for ncmpi_create() can be any flags such as NC_CLOBBER (create or overwrite a file) or NC_NOCLOBBER (create only if the file does not exist). In the case of ncmpi_open(), the mode can be used to open a file as NC_WRITE (for modification) or NC_NOWRITE (read-only). The info object provides a mechanism to pass I/O hints such as alignments of variables and file layout. Hints are of type MPI_Info, and they are based on the same syntax as MPI-IO.

Close:

int ncmpi_close(int id)