MPI_Type_struct(3) Open MPI MPI_Type_struct(3)

MPI_Type_struct - Creates a struct data type -- use of this routine is deprecated.

#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)

INCLUDE 'mpif.h'

Number of blocks (integer) also number of entries in arrays array_of_types, array_of_displacements, and array_of_blocklengths.
Number of elements in each block (array).
Byte displacement of each block (array).
Type of elements in each block (array of handles to datatype objects).

New datatype (handle).
Fortran only: Error status (integer).

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.

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The MPI-1 Standard originally made vague statements about padding and alignment; this was intended to allow the simple definition of structures that could be sent with a count greater than one.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

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.

Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.


November 24, 2021 4.1.2