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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. Table 9 lists the DataBlade API accessor functions that obtain information from a type descriptor.

Table 9. Data Type Information in 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( )
Important:
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 may change in future releases. Therefore, to create portable code, always use the accessor functions in Table 9 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 IBM Informix: DataBlade API Function Reference

Obtaining Column Information
To obtain the source type of a distinct type Description of mi_get_type_source_type( ) in the IBM 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 IBM 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 IBM Informix: DataBlade API Function Reference

Looking Up Cast Functions
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