MPI_File_read_at(3)

NAME
MPI_File_read_at - Reads a file at an explicitly specified offset (blocking, noncollective).

SYNTAX

C Syntax
#include <mpi.h>
int MPI_File_read_at(MPI_File fh, MPI_Offset offset,
	void *buf, int count, MPI_Datatype datatype,
	MPI_Status *status)

Fortran Syntax (see FORTRAN 77 NOTES)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_READ_AT(FH, OFFSET, BUF, COUNT,
	DATATYPE, STATUS, IERROR)
	<type>	BUF(*)
	INTEGER	FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE), IERROR
	INTEGER(KIND=MPI_OFFSET_KIND)	OFFSET

Fortran 2008 Syntax
USE mpi_f08
MPI_File_read_at(fh, offset, buf, count, datatype, status, ierror)
	TYPE(MPI_File), INTENT(IN) :: fh
	INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: offset
	TYPE(*), DIMENSION(..) :: buf
	INTEGER, INTENT(IN) :: count
	TYPE(MPI_Datatype), INTENT(IN) :: datatype
	TYPE(MPI_Status) :: status
	INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax
#include <mpi.h>
void MPI::File::Read_at(MPI::Offset offset, void* buf,
	int count, const MPI::Datatype& datatype,
	MPI::Status& status)

void MPI::File::Read_at(MPI::Offset offset, void* buf,
	int count, const MPI::Datatype& datatype)

INPUT PARAMETERS

fh  File handle (handle).

offset
    File offset (integer).

count
    Number of elements in buffer (integer).

datatype
    Data type of each buffer element (handle).

OUTPUT PARAMETERS

buf Initial address of buffer (choice).

status
    Status object (status).

IERROR
    Fortran only: Error status (integer).

DESCRIPTION

MPI_File_read_at attempts to read from the file associated with fh (at the offset position) a total number of count data items having datatype type into the user's buffer buf. The offset is in etype units relative to the current view. That is, holes are not counted when locating an offset. The data is taken out of those parts of the file specified by the current view. MPI_File_read_at stores the number of datatype elements actually read in status. All other fields of status are undefined. It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened.

FORTRAN 77 NOTES
The MPI standard prescribes portable Fortran syntax for the OFFSET argument only for Fortran 90. FORTRAN 77 users may use the non-portable syntax

     INTEGER*MPI_OFFSET_KIND OFFSET

where MPI_OFFSET_KIND is a constant defined in mpif.h and gives the length of the declared integer in bytes.

ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.

Before the error value is returned, the current MPI error handler is called. For MPI I/O function errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler may be changed with MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that MPI does not guarantee that an MPI program can continue past an error.