# 4.16. Canonical MPI_PACK and MPI_UNPACK

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These functions read/write data to/from the buffer in the ``external32'' data format specified in Section External Data Representation: ``external32'' , 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.

MPI_PACK_EXTERNAL(datarep, inbuf, incount, datatype, outbuf, outsize, position )
IN datarep | data representation (string)
IN inbuf | input buffer start (choice)
IN incount | number of input data items (integer)
IN datatype | datatype of each input data item (handle)
OUT outbuf | output buffer start (choice)
IN outsize | output buffer size, in bytes (integer)
INOUT position | current position in buffer, in bytes (integer)

`int MPI_Pack_external(char *datarep, void *inbuf, int incount, MPI_Datatype datatype, void *outbuf, MPI_Aint outsize, MPI_Aint *position)
`

`MPI_PACK_EXTERNAL(DATAREP, INBUF, INCOUNT, DATATYPE, OUTBUF, OUTSIZE, POSITION, IERROR)
INTEGER INCOUNT, DATATYPE, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) OUTSIZE, POSITION
CHARACTER*(*) DATAREP
<type> INBUF(*), OUTBUF(*)
`

`void MPI::Datatype::Pack_external(const char* datarep, const void* inbuf, int incount, void* outbuf, MPI::Aint outsize, MPI::Aint& position) const
`

MPI_UNPACK_EXTERNAL(datarep, inbuf, incount, datatype, outbuf, outsize, position )
IN datarep | data representation (string)
IN inbuf | input buffer start (choice)
IN insize | input buffer size, in bytes (integer)
INOUT position | current position in buffer, in bytes (integer)
OUT outbuf | output buffer start (choice)
IN outcount | number of output data items (integer)
IN datatype | datatype of output data item (handle)

`int MPI_Unpack_external(char *datarep, void *inbuf, MPI_Aint insize, MPI_Aint *position, void *outbuf, int outcount, MPI_Datatype datatype)
`

`MPI_UNPACK_EXTERNAL(DATAREP, INBUF, INSIZE, POSITION, OUTBUF, OUTCOUNT, DATATYPE, IERROR)
INTEGER OUTCOUNT, DATATYPE, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) INSIZE, POSITION
CHARACTER*(*) DATAREP
<type> INBUF(*), OUTBUF(*)
`

`void MPI::Datatype::Unpack_external(const char* datarep, const void* inbuf, MPI::Aint insize, MPI::Aint& position, void* outbuf, int outcount) const
`

MPI_PACK_EXTERNAL_SIZE( datarep, incount, datatype, size )
IN datarep | data representation (string)
IN incount | number of input data items (integer)
IN datatype | datatype of each input data item (handle)
OUT size | output buffer size, in bytes (integer)

`int MPI_Pack_external_size(char *datarep, int incount, MPI_Datatype datatype, MPI_Aint *size)
`

`MPI_PACK_EXTERNAL_SIZE(DATAREP, INCOUNT, DATATYPE, SIZE, IERROR)
INTEGER INCOUNT, DATATYPE, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) SIZE
CHARACTER*(*) DATAREP
`

`MPI::Aint MPI::Datatype::Pack_external_size(const char* datarep, int incount) const
`

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