MPI_INFO_GET_VALUELEN(3)

📦
version 5.0.11 · 17 versions
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💅 MPI_INFO_GET_VALUELEN(3) — like, the Open MPI girlies' guide

okay so bestie, you know how an MPI_Info object is basically a little dictionary of key/value pairs? this page is about the glow-up move where you peek at a value's length without actually grabbing the value. iconic behavior, no notes. the manual page is MPI_INFO_GET_VALUELEN, and it lives in the Open MPI fam. 🎀

lowkey the whole point: MPI_Info_get_valuelen retrieves the length of the key value associated with an info object. that's the vibe. periodt.

✨ SYNTAX ✨

🩵 C Syntax

#include <mpi.h>

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

💜 Fortran Syntax

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

🦋 Fortran 2008 Syntax

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

🌸 INPUT PARAMETERS 🌸

  • info — the Info object, handle-style. your little dictionary bestie 💖
  • key — the key, as a string. the lookup word, iykyk

🎀 OUTPUT PARAMETERS 🎀

  • valuelen — length of the value arg (integer). the number you came for 🍓
  • flag — returns true if the key is defined, false if not (boolean). the vibes check 💅
  • ierror — Fortran only: error status (integer).

🔥 DESCRIPTION 🔥

MPI_Info_get_valuelen retrieves the length of the value associated with key. super straightforward, honestly.

  • if key is defined → valuelen gets set to the length of its associated value, and flag gets set to true ✅
  • if key is not defined → valuelen is literally not touched (hands off, it stays exactly as it was, don't come for it) and flag gets set to false 🙈
heads up: the length returned in C does not include the end-of-string character. so it's giving "just the content, ma'am" ✨
🚨 also important: if key is larger than MPI_MAX_INFO_KEY, the call is erroneous. do not do that. it's not cute.

💀 ERRORS 💀

ngl, almost all MPI routines return an error value — C routines hand it back as the return result of the function, and Fortran routines drop it in the last argument.

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 first. 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. simple as that 🫶

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. that 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. that's the whole rule, no cap. 📜

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

  • MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. yeah. all of them. 💀
  • 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. context matters, bestie.
  • 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, it might just be over. do not assume you're getting back up. 😭

see the MPI man page for a full list of MPI error codes. and see the Error Handling section of the MPI-3.1 standard for more information. go read it, it's good for you 🧚

🌈 SEE ALSO 🌈

  • MPI_Info_get
  • MPI_Info_get_nkeys
  • MPI_Info_get_nthkey

like, the whole info-object friend group. go say hi 👑

2003-2026, The Open MPI Community

okay that's the whole page, you ate that 🫶💖 version is from the Open MPI girlies themselves, dated Sep 11, 2026 — stay hydrated, go call MPI_Info_get_valuelen responsibly, and remember: valuelen doesn't include the end-of-string character, mwah 💋✨

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