MPI_Buffer_detach(3) Removes an existing buffer (for use in


#include <mpi.h>
int MPI_Buffer_detach(void *pbuf, int *psize)


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


The reason that MPI_Buffer_detach returns the address and size of the buffer being detached is to allow nested libraries to replace and restore the buffer. For example, consider

int size, mysize, idummy;
void *ptr, *myptr, *dummy;     
MPI_Buffer_detach(&ptr, &size);
MPI_Buffer_attach(myptr, mysize);
// ...library code...
MPI_Buffer_detach(&dummy, &idummy);
MPI_Buffer_attach(ptr, size);

This is much like the action of the Unix signal routine and has the same strengths (it is simple) and weaknesses (it only works for nested usages).

Note that for this approach to work, MPI_Buffer_detach must return MPI_SUCCESS even when there is no buffer to detach. In that case, it returns a size of zero. The MPI 1.1 standard for MPI_BUFFER_DETACH contains the text

The statements made in this section describe the behavior of MPI
for buffered-mode sends. When no buffer is currently associated,
MPI behaves as if a zero-sized buffer is associated with the

This could be read as applying only to the various Bsend routines. This implementation takes the position that this applies to MPI_BUFFER_DETACH as well.


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.

The Fortran binding for this routine is different. Because Fortran does not have pointers, it is impossible to provide a way to use the output of this routine to exchange buffers. In this case, only the size field is set.


Even though the pbuf argument is declared as void * , it is really the address of a void pointer (i.e., void ** ). See the rationale in the MPI Standard for more details.


For more information, please see the official MPI Forum web site, which contains the text of both the MPI-1 and MPI-2 standards. These documents contain detailed information about each MPI function (most of which is not duplicated in these man pages).


The LAM Team would like the thank the MPICH Team for the handy program to generate man pages ("doctext" from ), the initial formatting, and some initial text for most of the MPI-1 man pages.