datatype - type (handle)
true_lb - offset of the true lower bound of the type (integer).
true_extent - true extent of the type (integer).
The MPI_Type_get_true_extent() function is used to determine the true extent of a type datatype . This function will return the region of memory actually affected by a read or write of the data described by this type. This is described by the true lower bound, true_lb , and true extent, true_extent . These differ from the "effective" lower bound and extent of the type because a type may contain MPI_UB or MPI_LB which alter the effective values.
This function is useful because it allows one to allocate a buffer large enough to hold all the data of a type without having to pack it with the MPI_Pack() function.
PMPI_Type_get_true_extent() is the profiling version of this function.
All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.
In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.
MPI_SUCCESS - No error;
MPI_ERR_PENDING - Pending exception;
MPI_ERR_TYPE - Invalid data type;
MPI_ERR_ARG - Invalid pointer.
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