## 8.8.3. Datatypes

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The new functions for caching on datatypes are:

MPI_TYPE_CREATE_KEYVAL(type_copy_attr_fn, type_delete_attr_fn, type_keyval, extra_state)
IN type_copy_attr_fn | copy callback function for type_keyval (function)
IN type_delete_attr_fn | delete callback function for type_keyval (function)
OUT type_keyval | key value for future access (integer)
IN extra_state | extra state for callback functions

`int MPI_Type_create_keyval(MPI_Type_copy_attr_function *type_copy_attr_fn, MPI_Type_delete_attr_function *type_delete_attr_fn, int *type_keyval, void *extra_state)
`

`MPI_TYPE_CREATE_KEYVAL(TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN, TYPE_KEYVAL, EXTRA_STATE, IERROR)
EXTERNAL TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN
INTEGER TYPE_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
`

`static int MPI::Datatype::Create_keyval(MPI::Datatype::Copy_attr_function* type_copy_attr_fn, MPI::Datatype::Delete_attr_function* type_delete_attr_fn, void* extra_state)
`

The argument type_copy_attr_fn may be specified as MPI_TYPE_NULL_COPY_FN or MPI_TYPE_DUP_FN from either C, C++, or Fortran. MPI_TYPE_NULL_COPY_FN is a function that does nothing other than returning flag = 0 and MPI_SUCCESS. MPI_TYPE_DUP_FN is a simple-minded copy function that sets flag = 1, returns the value of attribute_val_in in attribute_val_out, and returns MPI_SUCCESS.

The argument type_delete_attr_fn may be specified as MPI_TYPE_NULL_DELETE_FN from either C, C++, or Fortran. MPI_TYPE_NULL_DELETE_FN is a function that does nothing, other than returning MPI_SUCCESS.

The C callback functions are:

`typedef int MPI_Type_copy_attr_function(MPI_Datatype oldtype, int type_keyval, void *extra_state, void *attribute_val_in, void *attribute_val_out, int *flag);
`

and

`typedef int MPI_Type_delete_attr_function(MPI_Datatype type, int type_keyval, void *attribute_val, void *extra_state);
`

The Fortran callback functions are:

`SUBROUTINE TYPE_COPY_ATTR_FN(OLDTYPE, TYPE_KEYVAL, EXTRA_STATE, ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
INTEGER OLDTYPE, TYPE_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE,
ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT
LOGICAL FLAG
`

and

`SUBROUTINE TYPE_DELETE_ATTR_FN(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE, IERROR)
INTEGER TYPE, TYPE_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL, EXTRA_STATE
`

The C++ callbacks are:

`typedef int MPI::Datatype::Copy_attr_function(const MPI::Datatype& oldtype, int type_keyval, void* extra_state, const void* attribute_val_in, void* attribute_val_out, bool& flag);
`

and

`typedef int MPI::Datatype::Delete_attr_function(MPI::Datatype& type, int type_keyval, void* attribute_val, void* extra_state);
`

MPI_TYPE_FREE_KEYVAL(type_keyval)
INOUT type_keyval | key value (integer)

`int MPI_Type_free_keyval(int *type_keyval)
`

`MPI_TYPE_FREE_KEYVAL(TYPE_KEYVAL, IERROR)
INTEGER TYPE_KEYVAL, IERROR
`

`static void MPI::Datatype::Free_keyval(int& type_keyval)
`

MPI_TYPE_SET_ATTR(type, type_keyval, attribute_val)
INOUT type | datatype to which attribute will be attached (handle)
IN type_keyval | key value (integer)
IN attribute_val | attribute value

`int MPI_Type_set_attr(MPI_Datatype type, int type_keyval, void *attribute_val)
`

`MPI_TYPE_SET_ATTR(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, IERROR)
INTEGER TYPE, TYPE_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL
`

`void MPI::Datatype::Set_attr(int type_keyval, const void* attribute_val)
`

MPI_TYPE_GET_ATTR(type, type_keyval, attribute_val, flag)
IN type | datatype to which the attribute is attached (handle)
IN type_keyval | key value (integer)
OUT attribute_val | attribute value, unless flag = false
OUT flag | false if no attribute is associated with the key (logical)

`int MPI_Type_get_attr(MPI_Datatype type, int type_keyval, void *attribute_val, int *flag)
`

`MPI_TYPE_GET_ATTR(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, FLAG, IERROR)
INTEGER TYPE, TYPE_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL
LOGICAL FLAG
`

`bool MPI::Datatype::Get_attr(int type_keyval, void* attribute_val) const
`

MPI_TYPE_DELETE_ATTR(type, type_keyval)
INOUT type | datatype from which the attribute is deleted (handle)
IN type_keyval | key value (integer)

`int MPI_Type_delete_attr(MPI_Datatype type, int type_keyval)
`

`MPI_TYPE_DELETE_ATTR(TYPE, TYPE_KEYVAL, IERROR)
INTEGER TYPE, TYPE_KEYVAL, IERROR
`

`void MPI::Datatype::Delete_attr(int type_keyval)
`

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