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Add documentation about calling version-1 C functions from C.

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Author: Florents Tselai <florents.tselai@gmail.com>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/90853055-5BBD-493D-91E5-721677C7C59B@gmail.com
This commit is contained in:
Tom Lane
2025-01-17 14:37:38 -05:00
parent 43830ecb8a
commit 86e4efc52b
3 changed files with 112 additions and 5 deletions
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20
src/tutorial/funcs.c
View File

@ -11,6 +11,7 @@
#include "postgres.h" /* general Postgres declarations */
#include "executor/executor.h" /* for GetAttributeByName() */
#include "utils/fmgrprotos.h" /* for text_starts_with() */
#include "utils/geo_decls.h" /* for point type */
PG_MODULE_MAGIC;
@ -102,6 +103,25 @@ concat_text(PG_FUNCTION_ARGS)
PG_RETURN_TEXT_P(new_text);
}
/* A wrapper around starts_with(text, text) */
PG_FUNCTION_INFO_V1(t_starts_with);
Datum
t_starts_with(PG_FUNCTION_ARGS)
{
text *t1 = PG_GETARG_TEXT_PP(0);
text *t2 = PG_GETARG_TEXT_PP(1);
Oid collid = PG_GET_COLLATION();
bool result;
result = DatumGetBool(DirectFunctionCall2Coll(text_starts_with,
collid,
PointerGetDatum(t1),
PointerGetDatum(t2)));
PG_RETURN_BOOL(result);
}
/* Composite types */
PG_FUNCTION_INFO_V1(c_overpaid);

24
src/tutorial/funcs.source
View File

@ -123,16 +123,25 @@ SELECT * FROM EMP;
-----------------------------
CREATE FUNCTION add_one(integer) RETURNS integer
AS '_OBJWD_/funcs' LANGUAGE C;
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
CREATE FUNCTION add_one(double precision) RETURNS double precision
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
CREATE FUNCTION makepoint(point, point) RETURNS point
AS '_OBJWD_/funcs' LANGUAGE C;
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
CREATE FUNCTION copytext(text) RETURNS text
AS '_OBJWD_/funcs' LANGUAGE C;
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
CREATE FUNCTION concat_text(text, text) RETURNS text
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
CREATE FUNCTION t_starts_with(text, text) RETURNS boolean
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
CREATE FUNCTION c_overpaid(EMP, integer) RETURNS boolean
AS '_OBJWD_/funcs' LANGUAGE C;
AS '_OBJWD_/funcs' LANGUAGE C STRICT;
SELECT add_one(3) AS four;
@ -140,6 +149,8 @@ SELECT makepoint('(1,2)'::point, '(3,4)'::point ) AS newpoint;
SELECT copytext('hello world!');
SELECT t_starts_with('foobar', 'foo');
SELECT name, c_overpaid(EMP, 1500) AS overpaid
FROM EMP
WHERE name = 'Bill' or name = 'Sam';
@ -147,10 +158,13 @@ WHERE name = 'Bill' or name = 'Sam';
-- remove functions that were created in this file
DROP FUNCTION c_overpaid(EMP, integer);
DROP FUNCTION t_starts_with(text, text);
DROP FUNCTION concat_text(text, text);
DROP FUNCTION copytext(text);
DROP FUNCTION makepoint(point, point);
DROP FUNCTION add_one(double precision);
DROP FUNCTION add_one(integer);
--DROP FUNCTION clean_EMP();
DROP FUNCTION clean_EMP();
DROP FUNCTION high_pay();
DROP FUNCTION new_emp();
DROP FUNCTION add_em(integer, integer);