Hi all, the exception on MPI_PACKED in the type matching rules (3.3.1) suggests, that one side of the communication can pack/unpack the message, while the other side reads/writes natively. I.e., is the following code valid MPI code? #include <mpi.h> #include <stdio.h> #include <stdlib.h> int main() { int A[100], B[10], psize; for (int i = 0; i < 100; i++) A[i] = i; MPI_Init(NULL, NULL); MPI_Pack_size(1, MPI_INT, MPI_COMM_SELF, &psize); void *parr = malloc(psize * 10); int pos = 0; for (int i = 0; i < 10; i++) MPI_Pack(&(A[i * 10]), 1, MPI_INT, parr, psize * 10, &pos, MPI_COMM_SELF); // Send the packed data and receive a contiguous buffer MPI_Sendrecv(parr, pos, MPI_PACKED, 0, 42, B, 10, MPI_INT, 0, 42, MPI_COMM_SELF, MPI_STATUS_IGNORE); for (int i = 0; i < 10; i++) printf("%i\n", B[i]); MPI_Finalize(); } Can the packed buffer include meta data? This would be reflected by a larger value in /pos/, right? Can this lead to unexpected message truncation? Thanks Joachim -- Dipl.-Inf. Joachim Protze IT Center Group: High Performance Computing Division: Computational Science and Engineering RWTH Aachen University Seffenter Weg 23 D 52074 Aachen (Germany) Tel: +49 241 80- 24765 Fax: +49 241 80-624765 [email protected] www.itc.rwth-aachen.de