IDXDesc (index descriptor)

The IDXDesc structure describes each index in a table. The same structure is used both in creating an index and inquiring about the index after a cursor is opened. The application does not specify the following fields in the index descriptor structure when creating an index: iRestrNum, bOutofDate, and iKeyLen.

The fields required in this structure vary by driver type and index type.

Note: The first three fields, szName, iIndexId, and szTagName are used to identify the index. A different combination of these three fields is used, depending on the driver type and on the specific index type. The rules are given below:

Driver Type	Index Type
Access	Either iIndexId or szName identifies the index.
dBASE	.NDX style: szName alone identifies the index.
	.MDX style: szName and szTagName together identify the index.
FoxPro	.CDX style: szName and szTagName together identify the index.
Paradox	Either iIndexId or szName identifies the index.
Text driver	Indexing not supported.
All SQL drivers	szName alone identifies the index. pszIndexName may be used to identify a pseudo-index.

The fields in this structure include:

Field	Type	Description
szName	DBITBLNAME	Specifies the index name.
iIndexId	UINT16	Specifies the number identifying the index.
szTagName	DBINAME	Specifies the index tag name. Supported for dBASE and FoxPro only.
szFormat	DBINAME	Currently, for information only. Describes the physical index format type (for example, BTREE or HASH).
bPrimary	BOOL16	TRUE, if the key is primary.
bUnique	BOOL16	TRUE, if the key is unique.
abDescending	BOOL16	An array of booleans describing whether the corresponding field in aiKeyFld is descending. Used only when bDescending is set to TRUE.
bDescending	BOOL16	TRUE, if the key is descending.
bMaintained	BOOL16	TRUE, if the key is maintained.
bSubset	BOOL16	TRUE, if the index is a subset index. Supported for dBASE and FoxPro only.
bExpIdx	BOOL16	TRUE, if the index is an expression index. Supported for dBASE and FoxPro only.
iCost	UINT16	Reserved.
iFldsInKey	UINT16	Specifies the number of key fields in a composite index. If the index is an expression, set to 0.
iKeyLen	UINT16	Not specified while index is created. Specifies the physical length of the key in bytes. The application developer needs to allocate a buffer of iKeyLen bytes to use as a key buffer. A key buffer is used with functions such as DbiExtractKey and DbiSetToKey.
bOutofDate	BOOL16	Not specified while index is created; TRUE, if the index is out-of-date.
iKeyExpType	UINT16	Specifies the type of the key expression (dBASE and FoxPro only). This value can be one of the following: fldDBCHAR, fldDBKEYNUM, or fldDBKEYBCD.
aiKeyFld	DBIKEY	Specifies an array of field numbers in the key.
szKeyExp	DBIKEYEXP	Specifies the key expression for an expression index (dBASE and FoxPro only). This field is used only if bExpIdx = TRUE. The expression is stated as a dBASE expression.
szKeyCond	DBIKEYEXP	Specifies the expression that defines the subset condition (dBASE and FoxPro only). This field is used only if bSubset = TRUE. The expression is stated as a dBASE expression.
bCaseInsensitive	BOOL16	TRUE, if the index is case-insensitive.
iBlockSize	UINT16	Specifies the internal block size in bytes for this index.
iRestrNum	UINT16	Not specified while index is created. Specifies the internal restructure number for this index. This number is set when the index descriptor is retrieved and should not be changed when passing the descriptor back to DbiDoRestructure.

Note:

The following four fields, explained in detail above, are used to describe the key for an index: iFldsInKey, aiKeyFld, bExpIdx, szKeyExp. The key is described by specifying either one of the following combinations:

For traditional indexes	For expression indexes
iFldsInKey and aiKeyFld	bExpIdx and szKeyExp