Thread: help wanted (fmgr.c)

I am a little stuck of a question.

In fmgr.c:1698, function "InputFunctionCall" at line 1718

/* Should get null result if and only if str is NULL */
if (str == NULL)
{........

What are we testing to be NULL here?
Do we expect str to changed at line 1715 
(  result = FunctionCallInvoke(&fcinfo);  )


Please advice,
Gevik.

At 2006-09-11 10:25:22 +0200, pgdev@xs4all.nl wrote:
>
> What are we testing to be NULL here?
> Do we expect str to changed at line 1715 

No. (Read the comment just above the function.)

The code is like this, starting from line 1703:
   if (str == NULL && flinfo->fn_strict)       return (Datum) 0;

That is, if the function is declared strict, and the argument (str) is
0, just return NULL straightaway. Then it sets up the fcinfo and calls
the function, and then:
   ...
   /* Should get null result if and only if str is NULL */   if (str == NULL)   {       if (!fcinfo.isnull)
 elog(ERROR, "input function %u returned non-NULL",                        fcinfo.flinfo->fn_oid);   }   else   {
if(fcinfo.isnull)               elog(ERROR, "input function %u returned NULL",
fcinfo.flinfo->fn_oid);  }
 

This says: If the argument is NULL and the input function didn't return
a NULL, log an error; but if the argument is non-NULL and the function
returned NULL, log this other error. (Note that a function would set
fcinfo->isnull to indicate that it wants to return an SQL NULL, as
explained in $DOC/plhandler.html)

-- ams

Thank you for your reply..... 
I found my bug in the code which made the function behave strangely.

On Mon, 2006-09-11 at 14:23 +0530, Abhijit Menon-Sen wrote:
> At 2006-09-11 10:25:22 +0200, pgdev@xs4all.nl wrote:
> >
> > What are we testing to be NULL here?
> > Do we expect str to changed at line 1715 
> 
> No. (Read the comment just above the function.)
> 
> The code is like this, starting from line 1703:
> 
>     if (str == NULL && flinfo->fn_strict)
>         return (Datum) 0;
> 
> That is, if the function is declared strict, and the argument (str) is
> 0, just return NULL straightaway. Then it sets up the fcinfo and calls
> the function, and then:
> 
>     ...
> 
>     /* Should get null result if and only if str is NULL */
>     if (str == NULL)
>     {
>         if (!fcinfo.isnull)
>                 elog(ERROR, "input function %u returned non-NULL",
>                          fcinfo.flinfo->fn_oid);
>     }
>     else
>     {
>         if (fcinfo.isnull)
>                 elog(ERROR, "input function %u returned NULL",
>                          fcinfo.flinfo->fn_oid);
>     }
> 
> This says: If the argument is NULL and the input function didn't return
> a NULL, log an error; but if the argument is non-NULL and the function
> returned NULL, log this other error. (Note that a function would set
> fcinfo->isnull to indicate that it wants to return an SQL NULL, as
> explained in $DOC/plhandler.html)
> 
> -- ams
>