Type descriptors
A type descriptor, MI_TYPE_DESC, is a DataBlade® API data type structure that contains information about an SQL data type. For built-in data types, this information comes from the syscolumns table. For extended data types, it contains the information in the sysxtdtypes table.
The following table lists the DataBlade® API accessor functions that obtain information from a type descriptor.
| Data type information | DataBlade® API accessor function |
|---|---|
| The alignment, in number of bytes, of the data type | mi_type_align() |
| Whether a value of the data type is passed by reference or passed by value | mi_type_byvalue() |
| A type descriptor for the element type of a collection data type | mi_type_element_typedesc() |
| The full name (owner.type_name) of the data type | mi_type_full_name() |
| The length of the data type | mi_type_length() |
| The maximum length of the data type | mi_type_maxlength() |
| The owner of the data type | mi_type_owner() |
| The precision (total number of digits) of the data type | mi_type_precision() |
| The qualifier of a DATETIME or INTERVAL data type | mi_type_qualifier() |
| The scale of a data type | mi_type_scale() |
| The short name (no owner) of the data type | mi_type_typedesc() |
| The type identifier for the data type | mi_typedesc_typeid() |
Restriction: To a DataBlade®
API module,
the type descriptor (MI_TYPE_DESC) is an opaque C data structure.
Do not access its internal fields directly. The internal structure
of MI_TYPE_DESC might change in future releases. Therefore,
to create portable code, always use the accessor functions in Data type
information in a type descriptor to obtain values from
this structure.
The DataBlade®
API uses
type descriptors in the following situations.
| Type descriptor usage | More information |
|---|---|
| To indicate a column type in a row descriptor | Description of mi_column_typedesc() in the Informix® DataBlade® API Function Reference |
| To obtain the source type of a distinct type | Description of mi_get_type_source_type() in the Informix® DataBlade® API Function Reference |
| To process returned row data, especially when not all the rows returned by a query have the same size and structure | Description of mi_get_row_desc_from_type_desc() in the Informix® DataBlade® API Function Reference |
| To identify a cast function by the source and target data types to generate its function descriptor | Description of mi_td_cast_get() in the Informix® DataBlade® API Function Reference |