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MPI_Pack - Pack a contiguous block of a type into a buffer


#include <mpi.h> int MPI_Pack(void *buf , int count , MPI_Datatype datatype , void *pack_buf , int pack_size , int *pos , MPI_Comm comm );

#include <pmpi.h> int PMPI_Pack(void *buf , int count , MPI_Datatype datatype , void *pack_buf , int pack_size , int *pos , MPI_Comm comm );

#include <mpi.h> void MPI::Datatype::Pack(const void *buf , int count , void *pack_buf , int pack_size , int &pos , const MPI::Comm &comm ) const;

INCLUDE 'mpif.h' MPI_PACK(buf , count , datatype , pack_buf , pack_size , pos , comm , ierr ) <type> buf (*), pack_buf (*) INTEGER count , datatype , pack_size , pos , comm , ierr


buf - buffer to pack from (array).

count - number of contiguous copies of type (integer)

datatype - type (handle)

pack_size - total size of pack_buf in bytes (integer)

pos - current offset into pack_buf (integer).

comm - communicator that only affects which error handler is called (handle)


pack_buf - buffer to pack into (array).

pos - current offset into pack_buf (integer).


The MPI_Pack() function is used to pack the data described by count contiguous copies of type datatype in buffer buf into the packed buffer pack_buf . The total size of the packed buffer is pack_size bytes. The current offset into the packed buffer is pos . This offset is updated when data is written into the packed buffer by this function.

The inverse of this function is MPI_Unpack(). The resulting packed data may be specified as of type MPI_PACKED and used in message passing functions.

Even though the communicator, comm is not directly used by this function, it should be a valid one (not MPI_COMM_NULL).

PMPI_Pack() is the profiling version of this function.


All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_TYPE - Invalid data type;

MPI_ERR_COUNT - Invalid count;

MPI_ERR_ARG - Invalid pointer.


MPI_Type_size (3) MPI_Pack_size (3) MPI_Unpack (3)

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