Statement's errorCode() returns an empty string before execution, and '00000' (five zeros) after a sucessfull execution:

<?php
$stmt = $pdo->prepare($query);
assert($stmt->errorCode === '');

$stmt->execute();
assert($stmt->errorCode === '00000');
?>

Neither this property nor the PDOStatement::errorInfo() properties are available if you create  your own exception handler.

I am using PHP 5.2.4, PDO_INFORMIX 1.2.0.

Making this call at any point in the program after setting your own exception handler produces an error:

PHP Notice:  Undefined property:  PDOStatement::$errorCode in new_query.php on line

or

PHP Notice:  Undefined property:  PDOStatement::$errorInfo in new_query.php on line

But if I set the PDO to SILENT, only set error codes with:

$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT)

Then process with if/else the call to this functions works fine.  The examples below only do error checking to show the result codes of this function.  Normally you would want more.

FAILS:

$dbh = new PDO("informix...")
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

try  {
      $result = $dbh->query("asdfkjasdfkjasdfjk");  /* obvious sql error */
      if ($result) print "success!";
      }
catch
      {
      $myeCode = $dbh->errorCode();
      /* do stuff with error */
      };

$dbh=0;

The error handler gets called but knows nothing about $dbh->errorCode or $dbh->errorInfo.

WORKS:

$dbh = new PDO("informix...")
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT);

$result = $dbh->query("asdfkjasdfkjasdfjk");  /* obvious sql error */
if ($result) 
      {
      /* process result */
      print "success!";

      /* all done, didn't make any changes */
      $dbh->rollback();
      }
else
      {
      $myeCode = $dbh->errorCode();
      print_r($myeCode);
      };

$dbh=0;  /* close connection */

I hope this helps someone else.
Cheers,
David