NAME¶
MPI_Type_struct - Creates a
struct data type -- use of this
routine is deprecated.
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
- 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The MPI-1 Standard originally made vague statements about padding and alignment;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 );
ERRORS¶
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.
SEE ALSO¶
MPI_Type_create_struct
MPI_Type_create_hindexed