MPI_FILE_WRITE(3)

💅 MPI_FILE_WRITE(3) 💅

okay bestie, welcome to Open MPI's page for MPI_File_write — the blocking, noncollective write that drops data at your individual file pointer, no group chat required ✨

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🌸 NAME 🌸

MPI_File_write — Writes a file starting at the location specified by the individual file pointer (blocking, noncollective).

blocking? yes. noncollective? yes. just you and the file, one-on-one, main character energy 👑

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_File_write(MPI_File fh, const void *buf,
     int count, MPI_Datatype datatype,
     MPI_Status *status)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_WRITE(FH, BUF, COUNT,
     DATATYPE, STATUS, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE), IERROR

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_File_write(fh, buf, count, datatype, status, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..), INTENT(IN) :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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💖 INPUT/OUTPUT PARAMETER 💖

• fh — File handle (handle). it's your file's little ID card 🪪

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🧚 INPUT PARAMETERS 🧚

• buf — Initial address of buffer (choice). where your data is chilling before it moves out 📦
• count — Number of elements in buffer (integer). how many of them are coming along 🍓
• datatype — Data type of each buffer element (handle). what kind of lil guys they are 🦋

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🌈 OUTPUT PARAMETERS 🌈

• status — Status object (status). the receipts, bestie 🧾
• ierror — Fortran only: Error status (integer). Fortran's way of saying "so how'd it go" 💀

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⭐ DESCRIPTION ⭐

okay so MPI_File_write attempts to write into the file associated with fh — right at the current individual file pointer position that the system is maintaining for you — a total number of count data items, having datatype type, from your buffer buf 🔥

The data gets written into those parts of the file specified by the current view. MPI_File_write stores the number of datatype elements actually written in status. All other fields of status are undefined. undefined! don't go reading into them, they're giving cryptic 🤫

⚠️ It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened. like, don't even try it, bestie 😭

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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. yes, Fortran's is that last IERROR slot you keep forgetting about 🫶

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. everybody out, no cap 💀
• 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. so specific, we love a handler with range 👑
• MPI_ERRORS_RETURN — Returns an error code to the application. the chill one, hands you the code and minds its business ✨

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. literally cannot stress this enough 🙈

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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okay that's the whole page bestie, you ate that 🫶💅 this was MPI_FILE_WRITE(3) from Open MPI, dated Sep 11, 2026 — go forth and write those files, blocking style, noncollective style, icon behavior only 🌟