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MPI_Type_struct(3) MPI MPI_Type_struct(3)

NAME

MPI_Type_struct - Creates a struct datatype

SYNOPSIS



int MPI_Type_struct(int count, int array_of_blocklengths[],
MPI_Aint array_of_displacements[],
MPI_Datatype array_of_types[], MPI_Datatype *newtype)










INPUT PARAMETERS



  

  
- number of blocks also number of entries in arrays array_of_types,
      array_of_displacements, and array_of_blocklengths (non-negative
    integer)

  

  
- number of elements in each block (non-negative integer)

  

  
- byte displacement of each block (integer)

  

  
- types of elements in each block (handle)
    

  








OUTPUT PARAMETERS



  

  
- new datatype (handle)
    

  








NOTES


If an upperbound is set explicitly by using the MPI datatype
    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The MPI standard originally made vague statements about padding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,


struct { int a; char b; } foo;


may have sizeof(foo) > sizeof(int) + sizeof(char) ; for
    example, sizeof(foo) == 2*sizeof(int) . The initial version of the
    MPI standard defined the extent of a datatype as including an epsilon
    that 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,
    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
    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 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; 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);










REMOVED FUNCTION


The current MPI standard defines this routine as removed. The user
    should use the replacement routine. The replacement for this routine is
    MPI_Type_create_struct .










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 guarantee that an MPI
    program can continue past an error; however, MPI implementations will
    attempt to continue whenever possible.





  

  
- No error; MPI routine completed successfully.

  

  
- Other error; use MPI_Error_string to get more information about
      this error code.
    

  









  

    2/9/2024