printTable API (was: Show INHERIT in \du)

On 25/03/2008, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> "Brendan Jurd" <direvus@gmail.com> writes:
>  > This makes me wonder whether print.c could offer something a bit more
>  > helpful to callers wishing to DIY a table; we could have a
>  > table-building struct with methods like addHeader and addCell.
>
> Once you have two occurrences of a pattern, it's reasonable to assume
>  there will be more later.  +1 for building a little bit of infrastructure.
>

Hi hackers,

Per the above discussion, I'm looking at creating a nice API in
print.c for callers wishing to build their own psql output table.

Currently, if you want to build your own table you need to implement
your own local version of the logic in printQuery.
describeOneTableDetails is the only place this happens right now, but
due to some localisation issues it looks like my \du patch will have
to build its table manually as well.

There seem to be some differences in the way printQuery and
describeOneTableDetails go about constructing the array of cells.
Here's the version from describe:

<code>   /* Generate table cells to be printed */   /* note: initialize all cells[] to NULL in case of error exit */
cells= pg_malloc_zero((numrows * cols + 1) * sizeof(*cells));
 
   for (i = 0; i < numrows; i++)   {       /* Name */
#ifdef WIN32       cells[i * cols + 0] = mbvalidate(PQgetvalue(res, i, 0), myopt.encoding);
#else       cells[i * cols + 0] = PQgetvalue(res, i, 0);    /* don't free this
             * afterwards */
 
#endif
       /* Type */
#ifdef WIN32       cells[i * cols + 1] = mbvalidate(PQgetvalue(res, i, 1), myopt.encoding);
#else       cells[i * cols + 1] = PQgetvalue(res, i, 1);    /* don't free this
             * either */
 
#endif
</code>

And the version from printQuery:

<code>   /* set cells */   ncells = ntuples * nfields;   cells = pg_local_calloc(ncells + 1, sizeof(*cells));
   i = 0;   for (r = 0; r < ntuples; r++)   {       for (c = 0; c < nfields; c++)       {           if
(PQgetisnull(result,r, c))               cells[i] = opt->nullPrint ? opt->nullPrint : "";           else           {
          cells[i] = (char *)                   mbvalidate((unsigned char *) PQgetvalue(result, r, c),
           opt->topt.encoding);
 
#ifdef ENABLE_NLS               if (opt->trans_columns && opt->trans_columns[c])                   cells[i] =
_(cells[i]);
#endif           }           i++;       }   }
</code>

So, it looks like:
1. describe malloc's the cells to zero, but print just does a local
calloc without any initialisation.
2. describe only does an mbvalidate for WIN32, but print does it in all cases.

Any opinions on which behaviour is preferable/more correct in these two cases?

Regards,
BJ