# MPI_Op_free

Frees a user-defined combination function handle

## Synopsis

    #include "mpi.h"
    int MPI_Op_free( MPI_Op *op )

## Input Parameter

op
  operation (handle)

## Notes

`op` is set to `MPI_OP_NULL` on exit.

## Null Handles

The MPI 1.1 specification, in the section on opaque objects, explicitly

## disallows freeing a null communicator. The text from the standard is

     A null handle argument is an erroneous IN argument in MPI calls, unless an
     exception is explicitly stated in the text that defines the function. Such
     exception is allowed for handles to request objects in Wait and Test calls
     (sections Communication Completion and Multiple Completions ). Otherwise, a
     null handle can only be passed to a function that allocates a new object and
     returns a reference to it in the handle.

## 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_Errhandler_set`; 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.

MPI_SUCCESS
  No error; MPI routine completed successfully.

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

MPI_ERR_ARG
  Invalid argument; the error code associated with this error indicates an attempt to free an MPI permanent operation (e.g., `MPI_SUM`). *N/ /*N MPI_ERR_PERM_KEY

MPI_ERR_ARG
  Invalid argument; the error code associated with this error indicates an attempt to free or chnage an MPI permanent keyval (e.g., `MPI_TAG_UB`). *N/ /*N MPI_ERR_UNKNOWN

MPI_ERR_UNKNOWN
  Unknown error. You should never see this. If you do, report it to `mpi-bugs@mcs.anl.gov`.

## See Also

MPI_Op_create

Location:opfree.c