Informix DataBlade API Programmer's Manual DataBlade API Function Descriptions

The mi_td_cast_get() function looks up a registered function by the type descriptors of its source and target data types and returns its function descriptor.

MI_FUNC_DESC *mi_td_cast_get(conn, source_tdesc, target_tdesc, cast_status)

MI_CONNECTION *conn;

MI_TYPE_DESC *source_tdesc;

MI_TYPE_DESC *target_tdesc;

mi_char *cast_status;

conn	is a pointer to the connection descriptor a previous call to mi_open(), mi_server_connect(), or mi_server_reconnect() has established.
source_tdesc	is a pointer to the type descriptor of the source data type of the cast, including its length and precision.
target_tdesc	is a pointer to the type descriptor of the target data type of the cast.
cast_status	is a pointer to the status flag that mi_td_cast_get() sets to indicate the kind of cast function that it has located.

Valid in Client LIBMI Application?	Valid in User-Defined Routine?
Yes	Yes

The mi_td_cast_get() function is the function whose source and target data types the source_tdesc and target_tdesc arguments references. It accepts source and target data types as pointers to type descriptors. This function is one of the functions of the Fastpath interface. It is a constructor function for the function descriptor.

The mi_td_cast_get() function performs the following tasks:

1. Looks in the syscasts system catalog table for the cast function that casts from the source_tdesc data type to the target_tdesc data type.
2. Allocates a function descriptor for the cast function and saves the routine sequence in this descriptor.
3. Allocates an MI_FPARAM structure for the cast function and saves the argument and return-value information in this structure.
4. Sets the cast_status function that was located.
5. Returns a pointer to the function descriptor that it allocated for the cast function.

The mi_td_cast_get() function allocates a new function descriptor in the PER_COMMAND memory duration.

The cast_status flag can have one of the following constant values.

The following call to mi_td_cast_get() looks for a cast function that converts from an INTEGER to an opaque data type called percent:

MI_TYPE_DESC *src_tdesc, *trgt_tdesc;

MI_COLLECTION *conn;

MI_FUNC_DESC *fdesc;

mi_char cast_stat;


src_tdesc = mi_typestring_to_typedesc(conn, "INTEGER");
trgt_tdesc = mi_typestring_to_typedesc(conn, "percent");
fdesc = mi_td_cast_td(conn, src_tdesc, trgt_tdesc,
	&cast_stat);
if ( fdesc == NULL )
	{
	switch ( cast_stat )
		{
		case MI_NO_CAST:
			mi_db_error_raise(NULL, MI_EXCEPTION,
				"No cast function found");
			break;
		case MI_ERROR_CAST:
			mi_db_error_raise(NULL, MI_EXCEPTION,
				"Error in mi_td_cast_get() function");
			break;
		case MI_NOP_CAST:

			mi_db_error_raise(NULL, MI_EXCEPTION,
				"No cast function needed");
			break;
		...

See the descriptions of the following functions: mi_cast_get(), mi_fparam_get(), mi_func_desc_by_typeid(), mi_routine_get(), mi_routine_exec(), and mi_routine_end().

For more information on the use of the Fastpath interface, see Calling UDRs with the Fastpath Interface.