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MPI_File_read_at(3) man page (version 1.8)

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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)


    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

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.


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