MPI_INFO_GET(3)

💖 MPI_INFO_GET 💖

okay bestie, so this is MPI_INFO_GET(3) from the Open MPI manual, and it's literally the "hey what's the value for this key" girlie of the info-object world. she reads, she doesn't write, she's ✨mysterious✨. let's get into it 🫶

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🌸 NAME 🌸

MPI_Info_get — retrieves the value associated with a key in an info object. that's it. that's the job. no cap.

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_Info_get(MPI_Info info, const char *key, int valuelen, char *value, int *flag)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_INFO_GET(INFO, KEY, VALUELEN, VALUE, FLAG, IERROR)
     INTEGER INFO, VALUELEN, IERROR
     CHARACTER*(*) KEY, VALUE
     LOGICAL FLAG

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_Info_get(info, key, valuelen, value, flag, ierror)
     TYPE(MPI_Info), INTENT(IN) :: info
     CHARACTER(LEN=*), INTENT(IN) :: key
     INTEGER, INTENT(IN) :: valuelen
     CHARACTER(LEN=valuelen), INTENT(OUT) :: value
     LOGICAL, INTENT(OUT) :: flag
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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💅 INPUT PARAMETERS 💅

• info — the Info object, aka a handle. she's the whole vibe container.
• key — the key, as a string. this is what you're asking about.
• valuelen — length of the value arg, as an integer. i.e. how much room you're offering her to write in.

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👑 OUTPUT PARAMETER 👑

• value — the value, as a string. this is the tea you came for.
• flag — returns true if the key is defined, false if not. a boolean, basically a yes/no girly.
• ierror — Fortran only: error status (integer).

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🦋 DESCRIPTION 🦋

so MPI_Info_get retrieves the value associated with key from a previous call to MPI_Info_set. if that key exists, she sets flag to true and hands you the value in value; otherwise she sets flag to false and leaves value unchanged. like, untouched. don't @ her.

valuelen is the number of characters available in value. if it's less than the actual size of the value, the returned value gets truncated 😭 — so size it properly, babe.

and for the C girlies specifically: valuelen should be one less than the amount of allocated space, to allow for the null terminator. do not forget the null terminator. she is watching. 👀

also, if key is larger than MPI_MAX_INFO_KEY, the call is erroneous. periodt.

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💀 ERRORS 💀

almost all MPI routines return an error value — C routines give it back as the return result of the function, and Fortran routines put it in the last argument. yeah, the last one. classic.

before the error value gets returned, the current MPI error handler associated with the communication object (think: communicator, window, file) is called. and if there's no communication object associated with the MPI call? then the call is considered attached to MPI_COMM_SELF and it'll 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 you're 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 via the mpi_initial_errhandler CLI argument to mpiexec, or via the 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 you can use:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic? yes. effective? 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, it 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, it aborts only the local process.
• MPI_ERRORS_RETURN — returns an error code to the application. very demure, very mindful.

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. 🙈

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.

see also:

• MPI_Info_create
• MPI_Info_delete
• MPI_Info_dup
• MPI_Info_free
• MPI_Info_get_valuelen
• MPI_Info_get_nkeys
• MPI_Info_get_nthkey
• MPI_Info_set

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🌈 Copyright 🌈

2003-2026, The Open MPI Community

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and that's the whole page bestie, you ate 💅✨ this was MPI_INFO_GET(3) from the Open MPI manual, dated Sep 10, 2026 — go forth and get those info values, ily 🫶🎀🦋