File: MPI_Type_struct.3

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.TH MPI_Type_struct 3 "2/18/1997" " " "MPI"
.SH NAME
MPI_Type_struct \-  Creates a struct datatype 
.SH SYNOPSIS
.nf
#include "mpi.h"
int MPI_Type_struct( count, blocklens, indices, old_types, newtype )
int           count;
int        blocklens[];
MPI_Aint      indices[];      
MPI_Datatype  old_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 blocklens 
- number of elements in each block (array)
.PD 1
.PD 0
.TP
.B indices 
- byte displacement of each block (array)
.PD 1
.PD 0
.TP
.B old_types 
- type of elements in each block (array 
of handles to datatype objects) 
.PD 1

.SH OUTPUT PARAMETER
.PD 0
.TP
.B newtype 
- new datatype (handle) 
.PD 1

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The MPI standard originally made vague statements about padding and alignment;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

.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_Errhandler_set
; 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.

.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_TYPE 
- Invalid datatype argument.  May be an uncommitted 
.PD 1
MPI_Datatype (see 
.I MPI_Type_commit
).
.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
.SH LOCATION
type_struct.c