# MPI_Type_indexed

## NAME

MPI_Type_indexed − Creates an indexed datatype.

## SYNTAX

## C Syntax

#include <mpi.h>
int MPI_Type_indexed(int count, int *array_of_blocklengths,

|  | int *array_of_displacements, MPI_Datatype oldtype,
|  | MPI_Datatype *newtype)

## Fortran Syntax

INCLUDE ’mpif.h’
MPI_TYPE_INDEXED(COUNT, ARRAY_OF_BLOCKLENGTHS,

|  |  | ARRAY_OF_DISPLACEMENTS, OLDTYPE, NEWTYPE, IERROR) |
|  | INTEGER |  | COUNT, ARRAY_OF_BLOCKLENGTHS(*)
|  | INTEGER |  | ARRAY_OF_DISPLACEMENTS(*), OLDTYPE, NEWTYPE
|  | INTEGER |  | IERROR

## C++ Syntax

#include <mpi.h>
Datatype Datatype::Create_indexed(int count,

| const int array_of_blocklengths[],
| const int array_of_displacements[]) const

## INPUT PARAMETERS

| count |  | Number of blocks -- also number of entries in array_of_displacements and array_of_blocklengths (nonnegative integer).

array_of_blocklengths

Number of elements per block (array of nonnegative integers).

array_of_displacements

Displacement for each block, in multiples of oldtype extent (array of integer).

| oldtype |  | Old datatype (handle). |

## OUTPUT PARAMETERS

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

## DESCRIPTION

The function MPI_Type_indexed allows replication of an old datatype into a sequence of blocks (each block is a concatenation of the old datatype), where each block can contain a different number of copies and have a different displacement. All block displacements are multiples of the old data type’s extent.

Example: Let oldtype have type map {(double, 0), (char, 8)}, with extent 16. Let B = (3, 1) and let D = (4, 0). A call to MPI_Type_indexed(2, B, D, oldtype, newtype) returns a datatype with type map

{(double, 64), (char, 72), (double, 80), (char, 88),
(double, 96), (char, 104),
(double, 0), (char, 8)}

That is, three copies of the old type starting at displacement 4 x 16 = 64, and one copy starting at displacement 0.

In general, assume that oldtype has type map

{(type(0), disp(0)), ..., (type(n-1), disp(n-1))},

with extent ex. Let B be the array_of_blocklength argument and D be the array_of_displacements argument. The newly created datatype has
n x S ^count-1
i = 0 B[i] entries:

{(type(0), disp(0) + D[0]* ex), ...,
(type(n-1), disp(n-1) + D[0]* ex), ...,
(type(0), disp(0) + (D[0] + B[0]-1)* ex), ...,
(type(n-1), disp(n-1) + (D[0]+ B[0]-1)* ex), ...,
(type(0), disp(0) + D[count-1]* ex), ...,
(type(n-1), disp(n-1) + D[count-1]* ex), ...,
(type(0), disp(0) + (D[count-1] + B[count-1] -1)* ex), ...,
(type(n-1), disp(n-1) + (D[count-1] + B[count-1] -1)* ex)}

A call to MPI_Type_vector(count, blocklength, stride, oldtype, newtype) is equivalent to a call to MPI_Type_indexed(count, B, D, oldtype, newtype) where

D[j] = j * stride, j = 0,..., count-1

and

B[j] = blocklength, j = 0, .., count-1

## 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_hindexed
MPI_Type_hindexed

MPI API Index