SYNTAX

C Syntax

#include <mpi.h>
int MPI_Type_struct(int count, int *array_of_blocklengths,
        MPI_Aint *array_of_displacements, MPI_Datatype *array_of_types,
        MPI_Datatype *newtype)

Fortran Syntax

INCLUDE 'mpif.h'
MPI_TYPE_STRUCT(COUNT, ARRAY_OF_BLOCKLENGTHS,
                ARRAY_OF_DISPLACEMENTS, ARRAY_OF_TYPES,
                NEWTYPE, IERROR)
        INTEGER COUNT, ARRAY_OF_BLOCKLENGTHS(*)
        INTEGER ARRAY_OF_DISPLACEMENTS(*)
        INTEGER ARRAY_OF_TYPES(*), NEWTYPE, IERROR 

INPUT PARAMETERS

count

Number of blocks (integer) also number of entries in arrays array_of_types, array_of_displacements, and array_of_blocklengths.

array_of_blocklengths

Number of elements in each block (array).

array_of_displacements

Byte displacement of each block (array).

array_of_types

Type of elements in each block (array of handles to datatype objects).

OUTPUT PARAMETERS

newtype

New datatype (handle).

IERROR

Fortran only: Error status (integer).

DESCRIPTION

Note that use of this routine is deprecated as of MPI-2. Use MPI_Type_create_struct instead.

This deprecated routine is not available in C++.

MPI_Type_struct is the most general type constructor. It further generalizes MPI_Type_hindexed in that it allows each block to consist of replications of different datatypes.

Example: Let type1 have type map

    {(double, 0), (char, 8)}

with extent 16. Let B = (2, 1, 3), D = (0, 16, 26), and T = (MPI_FLOAT, type1, MPI_CHAR). Then a call to MPI_Type_struct(3, B, D, T, newtype) returns a datatype with type map

    {(float, 0), (float,4), (double, 16), (char, 24), 
    (char, 26), (char, 27), (char, 28)}

That is, two copies of MPI_FLOAT starting at 0, followed by one copy of type1 starting at 16, followed by three copies of MPI_CHAR, starting at 26. (We assume that a float occupies 4 bytes.)

For more information, see section 3.12.1 of the MPI-1.1 Standard.

NOTES

If an upperbound is set explicitly by using the MPI datatype MPI_UB, the corresponding index must be positive.

The MPI-1 Standard originally made vague statements about padding and alignment; this was intended to allow the simple definition of structures that could be sent with a count greater than one.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,

    struct {int a; char b;} foo;

may have

    sizeof(foo) = sizeof(int) + sizeof(char); 

defining the extent of a datatype as including an epsilon, which would have allowed an implementation to make the extent an MPI datatype 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 datatype 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 );