MPI_TYPE_SIZE_X(3)

💖 MPI_TYPE_SIZE_X(3) — the Open MPI glow-up 💖

okay bestie, so this is a page from the Open MPI manual and it's literally about figuring out how many bytes your datatype is eating. two functions, one mission: MPI_Type_size and MPI_Type_size_x. let's get into it 🎀

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✨ NAME ✨

MPI_Type_size, MPI_Type_size_x — Returns the number of bytes occupied by entries in a data type.

like, the byte count. the whole vibe check of your datatype's size. 💅

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🌸 SYNTAX 🌸

💜 C Syntax

#include <mpi.h>

int MPI_Type_size(MPI_Datatype datatype, int *size)
int MPI_Type_size_x(MPI_Datatype datatype, MPI_Count *size)

💜 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_SIZE(DATATYPE, SIZE, IERROR)
     INTEGER DATATYPE, SIZE, IERROR
MPI_TYPE_SIZE_X(DATATYPE, SIZE, IERROR)
     INTEGER DATATYPE
        INTEGER(KIND=MPI_COUNT_KIND) SIZE
        INTEGER IERROR

💜 Fortran 2008 Syntax

USE mpi_f08
MPI_Type_size(datatype, size, ierror)
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     INTEGER, INTENT(OUT) :: size
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Type_size_x(datatype, size, ierror)
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     INTEGER(KIND=MPI_COUNT_KIND), INTENT(OUT) :: size
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🦋 INPUT PARAMETER 🦋

• datatype — Datatype (handle). yes it's a handle, no you can't just pass vibes. 🫶

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🌈 OUTPUT PARAMETERS 🌈

• size — Datatype size (integer). the moment of truth, bestie ✨
• ierror — Fortran only: Error status (integer). Fortran girlies get their own lil error slot 💜

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👑 DESCRIPTION 👑

okay so here's the tea ☕ — MPI_Type_size returns the total size, in bytes, of the entries in the type signature associated with datatype; i.e., the total size of the data in a message that would be created with this datatype. so like, if you sent a message with this datatype, this is how much data is actually in there. 📦

and the important bit: entries that occur multiple times in the datatype are counted with their multiplicity. so if something shows up three times, it counts three times. no shortcuts, no "oops i only counted it once". fr fr. 🔥

for either function, if the size 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. so yeah — too small to hold the number? you get the MPI_UNDEFINED energy instead. 💀

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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.

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. 😭 everything goes down together, no survivors.
• 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, hands you the error and lets you deal 💅

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 assume you can just walk it off, 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.

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🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

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and that's the whole page, no cap 🧚✨ mwah 💋 — written by the Open MPI Community, dated Sep 11, 2026, from the Open MPI era of the manual. go forth and count your bytes, queen 👑🍓