MPI_TYPE_STRUCT(3)MPI_TYPE_STRUCT(3)NAMEMPI_Type_struct - Creates a struct datatype
SYNOPSIS
C:
#include <mpi.h>
int MPI_Type_struct( count, blocklens, indices, old_types,
newtype )
int count;
int blocklens[];
MPI_Aint indices[];
MPI_Datatype old_types[];
MPI_Datatype *newtype;
C++:
#include <mpi.h>
Datatype Datatype::Create_struct(
int count,
const int array_of_blocklengths[],
const Aint array_of_displacements[],
const Datatype array_of_types[])
Fortran:
INCLUDE "mpif.h" (or USE MPI)
INTEGER count, array_of_blocklengths(*),
array_of_displacements(*), array_of_types(*),
newtype, ierror
CALL MPI_TYPE_STRUCT(count, array_of_blocklengths(*),
array_of_displacements(*), array_of_types(*),
newtype, ierror)
STANDARDS
This release implements the MPI 1.2 standard, as documented by the MPI
Forum in the spring 1997 release of MPI: A Message Passing Interface
Standard.
DESCRIPTION
The MPI_Type_struct routine creates a struct data type. This routine
accepts the following parameters:
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MPI_TYPE_STRUCT(3)MPI_TYPE_STRUCT(3)
count Specifies the number of blocks. Also specifies the number
of entries in old_types, indices, and blocklens.
blocklens Specifies the number of elements in each block (array).
indices Specifies the byte displacement of each block (array).
old_types Specifies the type of elements in each block (array of
handles to data type objects).
newtype Returns the new data type (handle).
ierror Specifies the return code value for successful completion,
which is in MPI_SUCCESS. MPI_SUCCESS is defined in the
mpif.h file.
NOTES
If an upper bound is set explicitly by using the MPI data type MPI_UB,
the corresponding index must be positive.
The MPI standard originally made vague statements about padding and
alignment; this was intended to allow the simple definition of structures
that could be sent with a count greater than one. For example, in the
structure definition, struct { int a; char b; } foo;, the sizeof value
might be sizeof(foo) > sizeof(int) + sizeof(char) (for example,
sizeof(foo) == 2*sizeof(int)). The initial version of the MPI standard
defined the extent of a data type as including an epsilon that would have
allowed an implementation to make the extent an MPI data type for this
structure equal to 2*sizeof(int). However, since different systems might
define different paddings, a clarification to the standard made epsilon
zero. Thus, if you define a structure data type and wish to send or
receive multiple items, you should explicitly include an MPI_UB entry as
the last member of the structure. For example, the following code can be
used for the structure foo:
blen[0] = 1; indices[0] = 0; oldtypes[0] = MPI_INT;
blen[1] = 1; indices[1] = &foo.b - &foo; oldtypes[1] = MPI_CHAR;
blen[2] = 1; indices[2] = sizeof(foo); oldtypes[2] = MPI_UB;
MPI_Type_struct( 3, blen, indices, oldtypes, &newtype );
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