Re: [HACKERS] strange behavior with C function and DEFAULT function parameters

[Andrew Dunstan]

On 10/20/2013 08:38 PM, Tomas Vondra wrote:
Hi,
I ran into some pretty strange behavior of C-language function and
default parameter values, both on 9.2 and 9.4devel. Consider for example
this trivial C function:

     Datum
     show_bug(PG_FUNCTION_ARGS) {
        elog(WARNING, "called ;-)");
        PG_RETURN_VOID();
     }

which is accessed using this definition:

     CREATE FUNCTION show_bug(a TEXT DEFAULT NULL)
     RETURNS void
     AS 'bug.so'
     LANGUAGE C STRICT;

and let's try various calls:

     db=# SELECT show_bug('a');
     WARNING: called ;-)
      show_bug
     ----------

      (1 row)

Seems ok. Now let's use the default value:

     db=# SELECT show_bug();
      show_bug
     ----------

      (1 row)

     db=# SELECT show_bug(NULL);
      show_bug
     ----------

      (1 row)

Well, seems quite strange to me - it seems as if the function is called,
but apparently it's not. I can't find anything relevant in the docs.

For comparison, a matching PL/pgSQL function:

     CREATE FUNCTION show_bug2(a TEXT DEFAULT NULL) RETURNS void AS $$
     BEGIN
         RAISE WARNING 'called ;-)';
     END;
     $$ LANGUAGE plpgsql;

which behaves exactly as expected in all three cases:

     db=# SELECT show_bug('a');
     WARNING: called ;-)
      show_bug
     ----------

      (1 row)

     db=# SELECT show_bug();
     WARNING: called ;-)
      show_bug
     ----------

      (1 row)
     db=# SELECT show_bug(NULL);
     WARNING: called ;-)
      show_bug
     ----------

      (1 row)

So, what I'm doing wrong? Seems like a bug to me ...


It's not a bug, it's expected. STRICT functions are not called with NULL 
inputs - the result of the function is instead taken as NULL.

cheers

andrew




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