MPI_FILE_GET_TYPE_EXTENT(3)

💅 MPI_FILE_GET_TYPE_EXTENT(3) — the Open MPI glow-up ✨

okay so bestie, this is a page from the Open MPI manual, section 3, and it's literally all about MPI_File_get_type_extent — yes that's a mouthful, we'll get through it together 🫶

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🌸 NAME 🌸

MPI_File_get_type_extent — returns the extent of the data type in a file. that's it, that's the vibe 💖

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_File_get_type_extent(MPI_File fh, MPI_Datatype
     datatype, MPI_Aint *extent)

🦋 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_GET_TYPE_EXTENT(FH, DATATYPE, EXTENT, IERROR)
     INTEGER FH, DATATYPE, IERROR
     INTEGER(KIND=MPI_ADDRESS_KIND)  EXTENT

🌈 Fortran 2008 Syntax

USE mpi_f08
MPI_File_get_type_extent(fh, datatype, extent, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: extent
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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💜 INPUT PARAMETERS 💜

• fh — the file handle, a.k.a. the handle kinda girl 👑 (it's a handle).
• datatype — the data type, also a handle 🎀.

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🍓 OUTPUT PARAMETERS 🍓

• extent — the data type extent (an integer, periodt).
• ierror — Fortran only: the error status (integer). no cap 🙈

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🌟 DESCRIPTION 🌟

okay so MPI_File_get_type_extent is literally the girlie you call to calculate the extent for datatype in the file 💅 the extent is the same for all processes accessing the file associated with fh — iconic, consistent, main character energy ✨

and here's the cute lil detail: if the current view uses a user-defined data representation, MPI_File_get_type_extent uses the dtype_file_extent_fn callback to calculate the extent. iykyk 🔥

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🧚 NOTES 🧚

ngl this part matters, so pay attention bestie 🫶 if the file data representation is anything other than “native,” you gotta be careful constructing etypes and file types. any of the data-type constructor functions may be used; however, for those functions that accept displacements in bytes, the displacements must be specified in terms of their values in the file for the file data representation being used. MPI will interpret these byte displacements as is — no scaling will be done, fr fr 💀

the function MPI_File_get_type_extent can be used to calculate the extents of data types in the file 🌸 for etypes and file types that are portable data types, MPI will scale any displacements in the data types to match the file data representation. but data types passed as arguments to read/write routines specify the data layout in memory, therefore they must always be constructed using displacements corresponding to displacements in memory 🎀 (memory layout ≠ file layout, don't mix them up, it's giving chaos 😭)

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💀 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, bestie.

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_thread, after 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 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_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 😭 dramatic but effective.
• 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 was called on that communicator. if called on a window or file, acts as if 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. the chill one ✨

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

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

note that MPI does not guarantee that an MPI program can continue past an error 👀 so like, don't count on it.

see the MPI man page for a full list of MPI error codes 📖

see the Error Handling section of the MPI-3.1 standard for more information 🧠

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

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and that's the whole page bestie, ate and left no crumbs 💅✨ this lil sign-off comes to you courtesy of the Open MPI crew, dated Sep 11, 2026, footer reading MPI_FILE_GET_TYPE_EXTENT(3) — slay 🎀🦋