Re: After upgrading libpq, the same function(PQftype) call returns a different OID

Let's not deviate from my request:

I have implemented various DB client modules using the C client APIs, for Oracle DB, SQL Server, IBM DB2, MySQL/MariaDB, SQLite and PostgreSQL.

While I like PostgreSQL a lot, this is the only case where I have to define myself the column type ids, to implement a "describe column" feature.

ODBC has SQLDescribeCol() / SQLDescribeColW() and predefined SQL_* constants like SQL_INTEGER, SQL_VARCHAR ...

Native PostgreSQL built-in SQL types should be listed in a .h header of the C client API

I do not want to execute SQL to identify a column type returned by PQftype().
This is not efficient, even if I would cache the mapping of the type oid to a type name.

I just want to do this:

static int prepareField(SqlStatement *st, int i)
{
int pgftype = PQftype(st->pgResult, i);
int pgfmod = PQfmod(st->pgResult, i);
...
switch (pgftype) {
case PG_TYPE_BOOL:
...
break;
case PG_TYPE_CHAR:
case PG_TYPE_BPCHAR:
case PG_TYPE_VARCHAR:
...
break;

And today I have to define all these type ids:

/* ! Should be provided by a PostgreSQL header file! */
#define PG_TYPE_BOOL 16
#define PG_TYPE_BYTEA 17
#define PG_TYPE_CHAR 18
#define PG_TYPE_NAME 19
#define PG_TYPE_INT8 20
#define PG_TYPE_INT2 21
#define PG_TYPE_INT2VECTOR 22
#define PG_TYPE_INT4 23
#define PG_TYPE_REGPROC 24
#define PG_TYPE_TEXT 25
#define PG_TYPE_OID 26
#define PG_TYPE_TID 27
#define PG_TYPE_XID 28
#define PG_TYPE_CID 29
...

I don't care if this list is generated when building PostgreSQL from sources.

I expect however that the type oids for built-in types remain the same forever.

Seb
________________________________
From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Sent: Wednesday, March 19, 2025 6:22 PM
To: Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
Cc: Sebastien Flaesch <sebastien(dot)flaesch(at)4js(dot)com>; M Tarkeshwar Rao <m(dot)tarkeshwar(dot)rao(at)ericsson(dot)com>; pgsql-general(at)postgresql(dot)org <pgsql-general(at)postgresql(dot)org>
Subject: Re: After upgrading libpq, the same function(PQftype) call returns a different OID

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Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
> On 3/18/25 23:41, Sebastien Flaesch wrote:
>> I was not expecting this file to be in a "server" folder, when it's to
>> be used for client apps.

> Not surprising. As I understand it this is the code used to build the
> type entries in the system catalog pg_type.

More the other way around: pg_type_d.h is built from the authoritative
source files pg_type.h and pg_type.dat, according to the process
described here:

https://urldefense.com/v3/__https://www.postgresql.org/docs/devel/bki.html__;!!I_DbfM1H!GM5pJKRPNVArTRiyYGhyIZrVAgLo7RZl1FSS5kG4IZvWLW75bP4zu1P7yVuLucHd3_FbuKym1-W3Wv0iEs6X$

>> And still, I do not trust the content.

Why not? If it's the "Backwards compatibility" comment that's
bothering you, a look at pg_type.h will show you that that's
only intended to apply to the CASHOID and LSNOID symbols.
Everything below that in pg_type_d.h is machine-generated.

regards, tom lane