Still "Stalled"? ECPG - varchar in struct?
От | William West |
---|---|
Тема | Still "Stalled"? ECPG - varchar in struct? |
Дата | |
Msg-id | OFF9D5DF25.8F847163-ON85256C05.004CD4D5@com обсуждение исходный текст |
Список | pgsql-interfaces |
Note: This is a re-send of a question that was 'stalled' due lack of author first establishing list membership. Apologies for the duplication, but it is unclear what has happened to/ will happen to the 'stalled' original. ======== I looked at comp.databases.postgresql.questions and posted a brief form of this question there. I am porting an existing Oracle/ PRO-C Application over to PostgreSQL 7.2.1 (ecpg 2.9.0). This application takes advantage of the fact that PRO-C lets you use 'varchar' as part of 'struct' definitions by re-writing 'varchar' during INCLUDE or DECLARE processing either one. This application can (and presently does) make a lot of use of: struct rowdef { ... /* Column */ varchar nameOFcolumn[maxlen] ; ... /* Column */ }; to define an interface buffer. PRO-C will re-write this, during EXEC SQL INCLUDE processing, as: struct rowdef { ... /* Column */ struct {int len; char arr[maxlen];} nameOFcolumn; ... /* Column */ }; This makes it possible to easily declare an I/O buffer that can hold many rows: EXEC SQL BEGIN DECLARE SECTION; struct rowdef ManyRows[25]; EXEC SQL END DECLARE SECTION; and code can easily refer to members of this buffer: /* Length column instance 7 */ ManyRows [7].nameOFcolumn.len; /* Address of column instance 7 */ ManyRows [7].nameOFcolumn.arr; or send them to other compile units: foo (ManyRows + 7); can run 'foo' on row 7 without 'foo' needing to be able to see the ManyRows DECLARE. The 'foo' compile unit only needs the INCLUDE to provide the 'rowdef' struct layout, since INCLUDE processing takes care of the C re-write that a varchar always needs. ==== It would appear that ecpg will only re-write a varchar if it is found in a DECLARE statement, because the varchar gets past the ecpg preprocessor's INCLUDE as-is ... and, of course, the real C compiler does not know what a 'varchar' is, so it complains. As a PostgreSQL 'newbie', I am not sure if it is more work to fix ecpg or to re-write how the application does things. I see it is a 'yacc' unit that handles the re-writing that ecpg now does, but I do not know 'yacc-ese' and do not know what else would be involved to fix ecpg to work like PRO-C? - Did I miss something here? - Any insights/ advice from the gurus? - Would it be a really big deal to support varchar re-writes during INCLUDE and not just during DECLARE?
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