MPI_TYPE_GET_EXTENT_X(3)

💖 MPI_Type_get_extent / MPI_Type_get_extent_x 💖

okay bestie, welcome to the Open MPI manual page for MPI_TYPE_GET_EXTENT_X(3) — yes the _x version is the main character here but her sibling MPI_Type_get_extent is literally right there too, they're a package deal fr fr.

This function returns the lower bound and extent of a data type. That's it, that's the whole vibe. 🦋

---

✨ SYNOPSIS ✨

🎀 C Syntax

#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

no cap, three whole syntaxes. pick your language bestie, they all slay 💅

---

🫶 INPUT PARAMETER

• datatype — the data type (a handle). that's the whole input, she's lowkey low-maintenance 👑

---

🌈 OUTPUT PARAMETERS

• lb — lower bound of the data type (integer).
• extent — data type extent (integer).
• ierror — Fortran only: error status (integer).

---

💜 DESCRIPTION

MPI_Type_get_extent returns the lower bound and the extent of datatype.

and for either function (yes, both of them, they share this trait 🫶): if either the lb or extent parameter cannot express the value to be returned — like, say, the parameter is too small to hold the output value — then it gets set to MPI_UNDEFINED. dramatic? maybe. but that's the rules. 💀

---

⭐ NOTE

bestie, listen to me: use MPI_Type_get_extent and it is strongly recommended over the legacy MPI-1 functions MPI_Type_extent and MPI_Type_lb. like, the old ones are giving ancient history. leave them in the past where they belong 🙈

---

🔥 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. classic split, iykyk.

Before that error value comes back to you, the current MPI error handler associated with the communication object (e.g., communicator, window, file) gets called. And 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 the info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. And 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. the lore is deep, we've been through it 🫠

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

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. she's the nuclear option 🔥
• 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 polite 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. like, do not assume you're gonna survive this one bestie, plan accordingly 😭

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

---

and that's the whole page, periodt 💅✨ huge shoutout to the Open MPI girlies and this page's source + version stamp, dated Sep 10, 2026 — MPI_TYPE_GET_EXTENT_X(3), we love her, we studied her, we aced the vibe check 🦋💖 no cap, go get those extents bestie 🫶