Returns \fIflag\fP = true if the communication associated with the status object
was canceled successfully. In such a case, all other fields of status (such as \fIcount\fP or \fItag\fP) are undefined. Otherwise, returns \fIflag\fP = false. If a receive operation might be canceled, one should call MPI_Test_cancelled first, to check whether the operation was canceled, before checking on the other fields of the return status.
.SH NOTES
Cancel can be an expensive operation that should be used only exceptionally.
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; 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.
