The Great and Terrible implementation of MPI-2

function index


Packs a datatype into contiguous memory, using the external32 format
int MPI_Pack_external(
  char *datarep,
  void *inbuf,
  int incount,
  MPI_Datatype datatype,
  void *outbuf,
  MPI_Aint outcount,
  MPI_Aint *position

int MPI_Pack_external(
  wchar_t *datarep,
  void *inbuf,
  int incount,
  MPI_Datatype datatype,
  void *outbuf,
  MPI_Aint outcount,
  MPI_Aint *position


[in] data representation (string)
[in] input buffer start (choice)
[in] number of input data items (integer)
[in] datatype of each input data item (handle)
[out] output buffer start (choice)
[in] output buffer size, in bytes (integer)
[in/out] current position in buffer, in bytes (integer)


These functions read/write data to/from the buffer in the "external32" data format, and calculate the size needed for packing. Their first arguments specify the data format, for future extensibility, but for MPI-2 the only valid value of the datarep argument is "external32."
Advice to users.

These functions could be used, for example, to send typed data in a portable format from one MPI implementation to another. ( End of advice to users.)

The buffer will contain exactly the packed data, without headers.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

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_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. 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; however, MPI implementations will attempt to continue whenever possible.

No error; MPI routine completed successfully.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).
Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.

Example Code

The following sample code illustrates MPI_Pack_external.

Insert code here.