.TH MPI_Type_struct 3 "11/12/2019" " " "MPI"

.SH NAME

MPI_Type_struct \-  Creates a struct datatype 

.SH SYNOPSIS

.nf

int MPI_Type_struct(int count,

int *array_of_blocklengths,

MPI_Aint * array_of_displacements,

MPI_Datatype * array_of_types, MPI_Datatype * newtype)

.fi

.SH INPUT PARAMETERS

.PD 0

.TP

.B count 

- number of blocks (integer) -- also number of

entries in arrays array_of_types ,

array_of_displacements  and array_of_blocklengths

.PD 1

.PD 0

.TP

.B array_of_blocklengths 

- number of elements in each block (array)

.PD 1

.PD 0

.TP

.B array_of_displacements 

- byte displacement of each block (array)

.PD 1

.PD 0

.TP

.B array_of_types 

- type of elements in each block (array

of handles to datatype objects)

.PD 1

.SH OUTPUT PARAMETERS

.PD 0

.TP

.B newtype 

- new datatype (handle)

.PD 1

.SH DEPRECATED FUNCTION

The MPI-2 standard deprecated a number of routines because MPI-2 provides

better versions.  This routine is one of those that was deprecated.  The

routine may continue to be used, but new code should use the replacement

routine.

The replacement for this routine is 

.I MPI_Type_create_struct

.SH NOTES

If an upperbound is set explicitly by using the MPI datatype 

.I MPI_UB

, the

corresponding index must be positive.

The MPI standard originally made vague statements about padding and alignment;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,

.nf

struct { int a; char b; } foo;

.fi

may have 

.I sizeof(foo) > sizeof(int) + sizeof(char)

; for example,

.I sizeof(foo) == 2*sizeof(int)

\&.

The initial version of the MPI standard

defined the extent of a datatype as including an 

.B epsilon

that would have

allowed an implementation to make the extent an MPI datatype

for this structure equal to 

.I 2*sizeof(int)

\&.

However, since different systems might define different paddings, there was

much discussion by the MPI Forum about what was the correct value of

epsilon, and one suggestion was to define epsilon as zero.

This would have been the best thing to do in MPI 1.0, particularly since

the 

.I MPI_UB

type allows the user to easily set the end of the structure.

Unfortunately, this change did not make it into the final document.

Currently, this routine does not add any padding, since the amount of

padding needed is determined by the compiler that the user is using to

build their code, not the compiler used to construct the MPI library.

A later version of MPICH may provide for some natural choices of padding

(e.g., multiple of the size of the largest basic member), but users are

advised to never depend on this, even with vendor MPI implementations.

Instead, if you define a structure datatype and wish to send or receive

multiple items, you should explicitly include an 

.I MPI_UB

entry as the

last member of the structure.  For example, the following code can be used

for the structure foo

.nf

blen[0] = 1; array_of_displacements[0] = 0; oldtypes[0] = MPI_INT;

blen[1] = 1; array_of_displacements[1] = &foo.b - &foo; oldtypes[1] = MPI_CHAR;

blen[2] = 1; array_of_displacements[2] = sizeof(foo); oldtypes[2] = MPI_UB;

MPI_Type_struct(3, blen, array_of_displacements, oldtypes, &newtype);

.fi

.SH 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 

.I malloc

or other non-MPICH runtime routines that are themselves not interrupt-safe.

.SH NOTES FOR FORTRAN

All MPI routines in Fortran (except for 

.I MPI_WTIME

and 

.I MPI_WTICK

) have

an additional argument 

.I ierr

at the end of the argument list.  

.I 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

.I call

statement.

All MPI objects (e.g., 

.I MPI_Datatype

, 

.I MPI_Comm

) are of type 

.I INTEGER

in Fortran.

.SH ERRORS

All MPI routines (except 

.I MPI_Wtime

and 

.I 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 

.I MPI_Comm_set_errhandler

(for communicators),

.I MPI_File_set_errhandler

(for files), and 

.I MPI_Win_set_errhandler

(for

RMA windows).  The MPI-1 routine 

.I MPI_Errhandler_set

may be used but

its use is deprecated.  The predefined error handler

.I MPI_ERRORS_RETURN

may be used to cause error values to be returned.

Note that MPI does 

.B not

guarentee that an MPI program can continue past

an error; however, MPI implementations will attempt to continue whenever

possible.

.PD 0

.TP

.B MPI_SUCCESS 

- No error; MPI routine completed successfully.

.PD 1

.PD 0

.TP

.B MPI_ERR_TYPE 

- Invalid datatype argument.  Additionally, this error can

occur if an uncommitted MPI_Datatype (see 

.I MPI_Type_commit

) is used

in a communication call.

.PD 1

.PD 0

.TP

.B MPI_ERR_COUNT 

- Invalid count argument.  Count arguments must be 

non-negative; a count of zero is often valid.

.PD 1

.PD 0

.TP

.B MPI_ERR_INTERN 

- This error is returned when some part of the MPICH 

implementation is unable to acquire memory.  

.PD 1