Attaches a user-defined buffer for sending


#include "mpi.h"
int MPI_Buffer_attach( buffer, size )
void *buffer;
int  size;

Input Parameters

buffer initial buffer address (choice)
size buffer size, in bytes (integer)


The size given should be the sum of the sizes of all outstanding Bsends that you intend to have, plus a few hundred bytes for each Bsend that you do. For the purposes of calculating size, you should use MPI_Pack_size. In other words, in the code
     MPI_Buffer_attach( buffer, size );
     MPI_Bsend( ..., count=20, datatype=type1,  ... );
     MPI_Bsend( ..., count=40, datatype=type2, ... );
the value of size in the MPI_Buffer_attach call should be greater than the value computed by
     MPI_Pack_size( 20, type1, comm, &s1 );
     MPI_Pack_size( 40, type2, comm, &s2 );
     size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;
The MPI_BSEND_OVERHEAD gives the maximum amount of space that may be used in the buffer for use by the BSEND routines in using the buffer. This value is in mpi.h (for C) and mpif.h (for Fortran).

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


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 the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

No error; MPI routine completed successfully.
Invalid buffer pointer. Usually a null buffer where one is not valid.
An internal error has been detected. This is fatal. Please send a bug report to

See Also

MPI_Buffer_detach, MPI_Bsend