MPI_TYPE_GET_EXTENT(3)

okay so this is the Open MPI manual page for MPI_TYPE_GET_EXTENT(3) — starring MPI_Type_get_extent and MPI_Type_get_extent_x — and it's literally here to explain lower bounds and extents. bestie, let's get into it 💅✨

✨ NAME ✨

MPI_Type_get_extent, MPI_Type_get_extent_x — Returns the lower bound and extent of a data type. periodt.

---

🌸 SYNTAX 🌸

💖 C Syntax

copy-paste exactly, no cap:

          #include <mpi.h>

          int MPI_Type_get_extent(MPI_Datatype datatype, MPI_Aint *lb,
               MPI_Aint *extent)
          int MPI_Type_get_extent_x(MPI_Datatype datatype, MPI_Count *lb,
               MPI_Count *extent)

🧚 Fortran Syntax

          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_TYPE_GET_EXTENT(DATATYPE, LB, EXTENT, IERROR)
               INTEGER DATATYPE, IERROR
               INTEGER(KIND=MPI_ADDRESS_KIND) LB, EXTENT
          MPI_TYPE_GET_EXTENT_X(DATATYPE, LB, EXTENT, IERROR)
               INTEGER DATATYPE, IERROR
               INTEGER(KIND=MPI_COUNT_KIND) LB, EXTENT

🦋 Fortran 2008 Syntax

          USE mpi_f08
          MPI_Type_get_extent(datatype, lb, extent, ierror)
               TYPE(MPI_Datatype), INTENT(IN) :: datatype
               INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: lb, extent
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror
          MPI_Type_get_extent_x(datatype, lb, extent, ierror)
               TYPE(MPI_Datatype), INTENT(IN) :: datatype
               INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: lb, extent
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

---

🎀 INPUT PARAMETER 🎀

• datatype — Data type (handle). it's giving "which data type are we checking?" energy, and honestly same.

---

💖 OUTPUT PARAMETERS 💖

• lb — Lower bound of data type (integer).
• extent — Data type extent (integer).
• ierror — Fortran only: Error status (integer).

---

🔥 DESCRIPTION 🔥

okay so MPI_Type_get_extent returns the lower bound and the extent of datatype. For either function — yes, _x is included — if either the lb or extent parameter cannot express the value to be returned (e.g., if the parameter is too small to hold the output value), it is set to MPI_UNDEFINED. that's the whole vibe.

---

👑 NOTE 👑

Use of MPI_Type_get_extent is strongly recommended over the legacy MPI-1 functions MPI_Type_extent and MPI_Type_lb. fr fr, this is the glow-up — use the recommended one.

---

💀 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. that's just how they do it, 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? yes. accurate? also yes.
• 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.

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. like, no promises, bestie 😭

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.

---

🌈 COPYRIGHT 🌈

2003-2026, The Open MPI Community

with all the love from the Open MPI girlies 💖 — copyright 2003-2026, The Open MPI Community, page date Sep 11, 2026, and you already know the page name: MPI_TYPE_GET_EXTENT(3). bye bestie, go get that extent! 🫶✨