The Great and Terrible implementation of MPI-2

function index


Find an MPI datatype matching a specified size
int MPI_Type_match_size(
  int typeclass,
  int size,
  MPI_Datatype *datatype


[in] generic type specifier (integer)
[in] size, in bytes, of representation (integer)
[out] datatype with correct type, size (handle)


typeclass is one of MPI_TYPECLASS_REAL, MPI_TYPECLASS_INTEGER and MPI_TYPECLASS_COMPLEX, corresponding to the desired typeclass. The function returns an MPI datatype matching a local variable of type ( typeclass, size ).

This function returns a reference (handle) to one of the predefined named datatypes, not a duplicate. This type cannot be freed. MPI_TYPE_MATCH_SIZE can be used to obtain a size-specific type that matches a Fortran numeric intrinsic type by first calling MPI_SIZEOF in order to compute the variable size, and then calling MPI_TYPE_MATCH_SIZE to find a suitable datatype. In C and C++, one can use the C function sizeof(), instead of MPI_SIZEOF. In addition, for variables of default kind the variable's size can be computed by a call to MPI_TYPE_GET_EXTENT, if the typeclass is known. It is erroneous to specify a size not supported by the compiler.

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.


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.

No error; MPI routine completed successfully.
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

Example Code

The following sample code illustrates MPI_Type_match_size.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>

 * type match size is part of the extended Fortran support

int main( int argc, char *argv[] )
    int errs = 0, err;
    int dsize;
    MPI_Datatype  newtype;

    MPI_Init( &argc, &argv );

    /* Check the most likely cases.  Note that it is an error to
       free the type returned by MPI_Type_match_size.  Also note
       that it is an error to request a size not supported by the compiler,
       so Type_match_size should generate an error in that case */
    MPI_Comm_set_errhandler( MPI_COMM_WORLD, MPI_ERRORS_RETURN );

    err = MPI_Type_match_size( MPI_TYPECLASS_REAL, sizeof(float), &newtype );
    if (err) {
    else {
        err = MPI_Type_size( newtype, &dsize );
        if (err) {
        else {
            if (dsize != sizeof(float)) {
                printf( "Unexpected size for float (%d != %d)\n", dsize, (intsizeof(float) );fflush(stdout);

    return errs;