# MPI_Unpack

Unpack a datatype into contiguous memory

## Synopsis

    #include "mpi.h"
    int MPI_Unpack ( void *inbuf, int insize, int *position,
       void *outbuf, int outcount, MPI_Datatype datatype,
       MPI_Comm comm )

## Input Parameters

| inbuf | input buffer start (choice)
| insize | size of input buffer, in bytes (integer)
| position | current position in bytes (integer)
| outcount | number of items to be unpacked (integer)
| datatype | datatype of each output data item (handle)
| comm | communicator for packed message (handle)

## Output Parameter

outbuf
  output buffer start (choice)

## 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.

## Errors

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.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_COMM
  Invalid communicator. A common error is to use a null communicator in a call (not even allowed in `MPI_Comm_rank`).

MPI_ERR_COUNT
  Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.

MPI_ERR_TYPE
  Invalid datatype argument. May be an uncommitted MPI_Datatype (see `MPI_Type_commit`).

MPI_ERR_ARG
  Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., `MPI_ERR_RANK`).

## See Also

MPI_Pack, MPI_Pack_size

Location:unpack.c