MPI_SIZEOF(3)

💖 NAME: MPI_Sizeof — Returns the size, in bytes, of the given type 💖

Okay bestie, this is the MPI_SIZEOF(3) page from the Open MPI manual — manual name folded in near the top like a little bow, no weird copied header line, periodt. ✨ The whole vibe: MPI_Sizeof returns the size, in bytes, of the given type. Slay. 💅

✨ SYNTAX ✨

Okay so here’s the Fortran situation, and yes both forms are showing up. 🫶

🧸 Fortran Syntax 🧸

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_SIZEOF(X, SIZE, IERROR)
<type>       X
INTEGER      SIZE, IERROR

🧚 Fortran 2008 Syntax 🧚

USE mpi_f08
MPI_Sizeof(x, size, ierror)
     TYPE(*), DIMENSION(..) :: x
     INTEGER, INTENT(OUT) :: size
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🍓 INPUT PARAMETER 🍓

• X — A Fortran variable of numeric intrinsic type (choice). Like, pick your numeric intrinsic fave, bestie. 💖

🎀 OUTPUT PARAMETERS 🎀

• SIZE — Size of machine representation of that type (integer). 💅
• ierror — Error status (integer). 🫶

🌈 DESCRIPTION 🌈

MPI_Sizeof returns the size (in bytes) of the machine representation of the given variable. It is a generic Fortran type and has a Fortran binding only — that means Fortran besties, this one’s for you. 💜 This routine is similar to the sizeof builtin in C. However — and this is the important plot twist — if given an array argument, it returns the size of the base element, not the size of the whole array. Do not get it twisted, bestie 😭.

🦋 NOTES 🦋

This function is not available in C because it is not necessary. Ngl, C doesn’t need it, so it’s not there. 💀

🔥 ERRORS 🔥

Okay bestie, error-handling lore time — stay with me, because this is the whole tea. ☕

Almost all MPI routines return an error value: C routines get it as the return result of the function, and Fortran routines get it 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 — collect them like stickers:

• 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 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. 🫶

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 💖

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That’s the whole page, bestie! This one is from Open MPI, dated Sep 11, 2026 — MPI_SIZEOF(3) says bye and hopes your sizes are always exactly what you expect. 💅✨