# MPI_Type_create_indexed_block

Create an indexed datatype with constant-sized blocks

## Synopsis

    int MPI_Type_create_indexed_block(int count,
                                   int blocklength,
                                   const int array_of_displacements[],
                                   MPI_Datatype oldtype,
                                   MPI_Datatype *newtype)

## Input Parameters

count
  length of array of displacements (integer)
blocklength
  size of block (integer)
array_of_displacements
  array of displacements (array of integer)
oldtype
  old datatype (handle)

## Output Parameters

newtype
  new datatype (handle)

## Notes

The indices are displacements, and are based on a zero origin. A common error is to do something like the following

        integer a(100)
        integer blens(10), indices(10)
        do i=1,10
    10       indices(i) = 1 + (i-1)*10
        call MPI_TYPE_CREATE_INDEXED_BLOCK(10,1,indices,MPI_INTEGER,newtype,ierr)
        call MPI_TYPE_COMMIT(newtype,ierr)
        call MPI_SEND(a,1,newtype,...)

expecting this to send "a(1),a(11),..." because the indices have values "1,11,...". Because these are displacements from the beginning of "a", it actually sends "a(1+1),a(1+11),...".

If you wish to consider the displacements as indices into a Fortran array, consider declaring the Fortran array with a zero origin

        integer a(0:99)

## Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as `malloc` or other non-MPICH runtime routines that are themselves not interrupt-safe.

## Notes for Fortran

All MPI routines in Fortran (except for `MPI_WTIME` and `MPI_WTICK`) have an additional argument `ierr` at the end of the argument list. `ierr` is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the `call` statement.

All MPI objects (e.g., `MPI_Datatype`, `MPI_Comm`) are of type `INTEGER` in Fortran.

## Errors

All MPI routines (except `MPI_Wtime` and `MPI_Wtick`) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with `MPI_Comm_set_errhandler` (for communicators), `MPI_File_set_errhandler` (for files), and `MPI_Win_set_errhandler` (for RMA windows). The MPI-1 routine `MPI_Errhandler_set` may be used but its use is deprecated. The predefined error handler `MPI_ERRORS_RETURN` may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS
  No error; MPI routine completed successfully.

MPI_ERR_TYPE
  Invalid datatype argument. May be an uncommitted MPI_Datatype (see `MPI_Type_commit`).

MPI_ERR_ARG
  Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., `MPI_ERR_RANK`).

Location:src/mpi/datatype/type_create_indexed_block.c