Date: Wed, 7 Feb 2001 11:00:38 -0500
From: Christopher Masto <chris@netmonger.net>
To: pgsql-interfaces@postgresql.org
Subject: An strftime function, and function name question
Message-ID: <20010207110038.A28372@netmonger.net>
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First of all, I have attached a simple-minded library I created to wrap 
the C strftime() function, since we needed some better date formatting 
and it seemed less cumbersome to do it on the server end.  I gave up C 
for Perl a couple of years ago, so I may be a bit rusty, but I tried to 
be careful with the buffers and strings. 
 
In any case, it works for my purposes.  I did also create a new typecast: 
 
CREATE FUNCTION int4 (timestamp) RETURNS int4 AS 
  'SELECT date_part(''epoch'', $1)::int4;' LANGUAGE 'sql';

because I wanted to be able to pass the Unix epoch time in, but I
didn't know what timestamps are internally.

My question is about naming.  I would like to be able to call this
function 'strftime'.  I've never created libraries before so it may
just be a lack of linker knowledge, but I couldn't see how to do that.
If I call it strftime, it obviously conflicts with the real strftime().
It would be nice if there were something like:

CREATE FUNCTION strftime(int4, varchar) RETURNS varchar AS
  '/usr/local/pgsql/lib/strftime.so' LANGUAGE 'c'
    USING C FUNCTION 'c_strftime';

I.e. some way to say "here's the name of the function in the library".

If there is, I didn't find it.
-- 
Christopher Masto         Senior Network Monkey      NetMonger Communications
chris@netmonger.net        info@netmonger.net        http://www.netmonger.net

Free yourself, free your machine, free the daemon -- http://www.freebsd.org/

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#include <string.h>
#include <time.h>

#include "postgres.h"
#include "utils/palloc.h"

typedef struct varlena varchar;

varchar *c_strftime(int now, varchar *fmt_in)
{
  char tmpbuf[128];
  char *fmt;
  struct tm *mytm;
  int len;
  int32 new_text_size;
  varchar *new_text;

  /* Copy incoming format string to null-terminated C string */
  fmt = (char *)palloc(VARSIZE(fmt_in) - VARHDRSZ + 1);
  memcpy((void *)fmt, (void *)VARDATA(fmt_in), VARSIZE(fmt_in) - VARHDRSZ);
  fmt[VARSIZE(fmt_in) - VARHDRSZ] = '\0';
  
  /* Call strftime().  XXX portability and buffer complications; see
     Perl source POSIX.xs for ideas. */
  mytm = localtime((const time_t *)&now);
  len = strftime(tmpbuf, sizeof tmpbuf, fmt, mytm);
  pfree(fmt);

  /* Copy the output into a Postgres varchar */
  new_text_size = len + VARHDRSZ;
  new_text = (varchar *)palloc(new_text_size);
  memset((void *)new_text, 0, new_text_size);
  VARSIZE(new_text) = new_text_size;

  if (len) {
    memcpy((void *)VARDATA(new_text), (void *)tmpbuf, len);
  }

  return new_text;
}

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