TransformSegment

Low-level key transformation.

Short Name

cttseg()

Type

Low-level function

Declaration

NINT TransformSegment(COUNT spos, COUNT mod, COUNT slen,

                      pTEXT target, pCOUNT aq, pConvMap mp);

Description

TransformSegment() transforms keys for low-level functions in the same manner that TransformKey() transforms for ISAM functions.

mod is the segment mode as described in “Key Segment Modes” in the c-tree Plus Programmer’s Reference Guide. slen is the length of the segment to transform. tarptr points to the key value to be transformed. Note that you can do a transformation on a portion of a key. aq points to an optional alternative collating sequence. mp points to an optional record schema. aq and mp can be NULL.

spos is only used if the segment mode requires the record schema. In this case, spos specifies which field of the schema is used to define the key segment type.

Return

TransformSegment() returns zero if successful, or a low-level error code if not. See “c-tree Plus Error Codes” in the c-tree Plus Programmer’s Reference Guide for a complete listing of valid c-tree Plus error values.

The following example transforms the double float key value pointed to by kvp in place.

Example

NINT      errc;

double    *kvp;

errc = TransformSegment(0,FLTSEG,8,(pTEXT) kvp,NULL,NULL);

Limitations

It is very important to note that transformations are done in place. Move the values to a buffer or structure specifically assigned to index building, rather than transforming variables in a record buffer. Taking the example code above, a mode of FLTSEG changes the format of the information stored in the double float variable so that it can be used by c-tree Plus as a key value. The information in that variable is no longer a valid double float value usable in C language calculations. If this variable was a part of a record structure, and it is written back to the data file, that portion of the data record is trashed.