MPI_Get_elements(3)

💖 MPI_Get_elements — bestie edition 💖

okay so this is from the MPI manual, section 3, and it's literally about counting how many basic elements you actually received. slay. let's get into it 🫶

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✨ NAME ✨

MPI_Get_elements — returns the number of basic elements 💅

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✨ SYNOPSIS ✨

int MPI_Get_elements(const MPI_Status *status, MPI_Datatype datatype,
int *count)

int MPI_Get_elements_c(const MPI_Status *status, MPI_Datatype datatype,
MPI_Count *count)

two flavors, bestie, pick your fighter 🎀

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✨ INPUT PARAMETERS ✨

• status — the return status of a receive operation (Status) 💌
• datatype — the datatype that was used by the receive operation (handle) 🌸

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✨ OUTPUT PARAMETERS ✨

• count — number of received basic elements (integer) ✨

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✨ NOTES ✨

okay so listen. if the size of the datatype is zero and the amount of data returned as determined by status is also zero, this routine will return a count of zero. and that's not a bug, that's a whole clarification made by the MPI Forum. so it's correct, it's intentional, it's giving consistency. periodt 💅

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✨ THREAD AND INTERRUPT SAFETY ✨

good news: this routine is thread-safe 🎉 which means you can absolutely let multiple threads run it at the same time, no user-provided thread locks required, no drama, no cap.

bad news: it is not interrupt safe 😭 and typically that's because of memory allocation routines like malloc or other non-MPICH runtime routines that are themselves not interrupt-safe. so like. keep that in mind 👑

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✨ NOTES FOR FORTRAN ✨

okay so Fortran besties, this one's for you 🌈

• all MPI routines in Fortran (except MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and it has the same meaning as the return value of the routine in C. 🍓
• in Fortran, MPI routines are subroutines, and they're invoked with the call statement.
• all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. yes, even those. 💜

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✨ ERRORS ✨

so ALL MPI routines (except MPI_Wtime and MPI_Wtick) return an error value — C routines as the value of the function, and Fortran routines in that last argument. 📢

before that value comes back to you, the current MPI error handler gets called. and by default, this error handler aborts the MPI job 💀 so yeah, that's a whole vibe check failure.

you can change the error handler with:

• MPI_Comm_set_errhandler (for communicators)
• MPI_File_set_errhandler (for files)
• MPI_Win_set_errhandler (for RMA windows)

the MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated ⚠️ so like, it's giving old news, don't.

if you want error values returned instead of your job getting nuked, the predefined error handler MPI_ERRORS_RETURN may be used. 🙈

note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. so like, sometimes it survives, sometimes it doesn't. no promises ✨

here's the error lineup 👇

• MPI_SUCCESS — no error; MPI routine completed successfully. 🎉 iconic.
• MPI_ERR_ARG — invalid argument. some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK). 😵
• MPI_ERR_TYPE — invalid datatype argument. additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit) is used in a communication call. 🚩
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code. 🔍

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🦋 SEE ALSO 🦋

okay there's genuinely not a SEE ALSO section on this page, bestie, so we're just gonna sit here and appreciate that MPI_Get_elements said "I am enough." queen behavior 👑

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that's the whole page fr fr 💖 this was the MPI manual, section 3, dated 4/10/2026 — and honestly, she ate. take care of your MPI_Status, count your elements, and don't let the default error handler end your whole career. bye bestie, ily 🫶✨💅