MPI_INFO_GET_STRING(3)

💖 MPI_INFO_GET_STRING ₍₃₎ — Open MPI, bestie edition 💖

okay so like. This is a section 3 page from Open MPI, and it's about MPI_Info_get_string — the glow-up version of digging a value out of an info object. She's giving "I have a key, do you have a value, let me check." Iconic. Let's go 🦋

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✨ NAME ✨

MPI_Info_get_string — retrieves the value associated with a key in an info object.

Like. That's it. That's the whole job. She finds stuff. 🎀

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Info_get_string(MPI_Info info, const char *key, int *buflen, char *value, int *flag)

🌸 Fortran Syntax

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

🌸 Fortran 2008 Syntax

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

Three flavors, one queen. Choose ur fighter 💅

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✨ INPUT PARAMETERS ✨

• info — the info object, aka the handle. ur little bag of keys and values 👜
• key — the key, as a string. the name tag on the thing you're looking for 🏷️

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✨ OUTPUT PARAMETER ✨

• buflen — okay so this one is doing double duty, main character behavior fr. On entry, it's the length of the value arg. On return, it gets set to the required size needed to hold the value string. It's an integer.
• value — the value. as a string. ✨
• flag — returns true if the key is defined, false if it's not. It's a boolean. 🚩
• ierror — Fortran only: the error status, an integer. 🫶

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✨ DESCRIPTION ✨

So MPI_Info_get_string retrieves the value associated with key from info, if any. That "if any" is doing a lot of heavy lifting, bestie, pay attention 👀

If such a key exists in info, she sets flag to true and returns the value in value. Gorgeous. Flawless. No notes.

Otherwise, she sets flag to false and leaves value unchanged. Not a single molecule moved. 💀

Now buflen — on input, it's the size of the provided buffer, for the output of buflen it's the size of the buffer needed to store the value string. And here's the tea: if the buflen passed into the function is less than the actual size needed to store the value string (including the null terminator in C), the value is truncated. So yes, she will absolutely cut ur string short if u didn't give her enough room. On return, buflen gets set to the required buffer size to hold the value string. She always tells u the truth about how much space she needed 🙈

If buflen is set to 0, value is not changed. Periodt.

In C, buflen includes the required space for the null terminator. In C, this function returns a null terminated string in all cases where the buflen input value is greater than 0. ✨ C stays needing that extra byte, iykyk.

⚠️ Also: if key is larger than MPI_MAX_INFO_KEY, the call is erroneous. So don't be sending her a novel when she asked for a key name. 🚨

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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. That's just how she operates.

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. So many layers. It's giving onion. 🧅

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

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. She said everyone. 💀
• 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. Selective chaos, we love a targeted queen 👑
• MPI_ERRORS_RETURN — returns an error code to the application. Polite! Mature! Handles it in-house 🫶

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

DIY era 💅 build ur own, we support it.

😭 Note that MPI does not guarantee that an MPI program can continue past an error. Like, no promises. She's honest about it.

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_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, we ate and left absolutely no crumbs 🍓✨ this little legend dropped Sep 10, 2026 and it's still MPI_INFO_GET_STRING(3) and still THAT girl 💖🦋🎀 slay, go read ur info objects, mwah 💜