17.2.414. MPI_Type_struct

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

17.2.414.1. SYNTAX

17.2.414.1.1. 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)

17.2.414.1.2. 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

17.2.414.2. 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).

17.2.414.3. OUTPUT PARAMETERS

  • newtype: New datatype (handle).

  • IERROR: Fortran only: Error status (integer).

17.2.414.4. DESCRIPTION

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

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.

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The MPI-1 Standard originally made vague statements about padding and alignment; this was intended to allow the simple definition of structures that could be sent with a count greater than one.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

17.2.414.6. ERRORS

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.

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.