MPI_FILE_READ_ORDERED(3)			     Open MPI				  MPI_FILE_READ_ORDERED(3)

MPI_File_read_ordered — Reads a file at a location specified by a shared file pointer (blocking, collective).

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_File_read_ordered(MPI_File fh, void *buf,
	       int count, MPI_Datatype datatype,
	       MPI_Status *status)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_FILE_READ_ORDERED(FH, BUF, COUNT, DATATYPE,
	       STATUS, IERROR)
	       <type>  BUF(*)
	       INTEGER FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE), IERROR

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

INPUT PARAMETERS
       • fh: File handle (handle).

       • 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_ordered  is  a  collective	 routine.  This	 routine  must	be  called by all processes in the
       communicator group associated with the file handle fh. Each process may pass different argument values  for
       the  datatype and count arguments. Each process attempts to read, from the file associated with fh, a total
       number of count data items having datatype type into the user’s buffer buf. For each process, the  location
       in  the	file  at  which	 data  is read is the position at which the shared file pointer would be after all
       processes whose ranks within  the  group	 are  less  than  that	of  this  process  had	read  their  data.
       MPI_File_read_ordered  returns  the  actual  number  of	datatype  elements read in status. The shared file
       pointer is updated by the amounts of data requested by all processes of the group.

ERRORS
       Almost all MPI routines return an error value; C routines as the return result of the function and  Fortran
       routines in the last argument.

       Before  the error value is returned, the current MPI error handler associated with the communication object
       (e.g., communicator, window, file) is called.  If no communication object is associated with the MPI  call,
       then  the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When
       MPI_COMM_SELF is not initialized (i.e.,	before	MPI_Init  <#mpi-init>/MPI_Init_thread  <#mpi-init-thread>,
       after  MPI_Finalize  <#mpi-finalize>,  or  when	using the Sessions Model exclusively) the error raises the
       initial error handler. The initial error handler can  be	 changed  by  calling  MPI_Comm_set_errhandler	<#
       mpi-comm-set-errhandler>	 on  MPI_COMM_SELF  when  using the World model, or the mpi_initial_errhandler CLI
       argument	 to  mpiexec  or  info	key   to   MPI_Comm_spawn   <#mpi-comm-spawn>/MPI_Comm_spawn_multiple	<#
       mpi-comm-spawn-multiple>.   If  no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error  handler  is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT  An  error handler that can be invoked on a communicator, window, file, or session. When
	 called on a communicator, it acts as if MPI_Abort <#mpi-abort> was called on that communicator. If called
	 on a window or file, acts as if MPI_Abort <#mpi-abort> was called on a communicator containing the  group
	 of processes in the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler	 <#mpi-comm-create-errhandler>	   then	    MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	<#mpi-file-create-errhandler>	  then	   MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				  MPI_FILE_READ_ORDERED(3)
