try and catch a warning

Answer 1

You should probably try to get rid of the warning completely, but if that's not possible, you can prepend the call with @ (i.e. @dns_get_record(...)) and then use any information you can get to figure out if the warning happened or not.

Answer 2

One possibility is to set your own error handler before the call and restore the previous error handler later with restore_error_handler(). Zend Framework does this at several locations. BTW there's was some discussion lately on the PHP newsgroup about replacing PHP errors with exceptions natively.

Another possibility is to suppress the call with the @ operator and check the return value of dns_get_record() afterwards.

sidenote

You can use set_error_handler() and the ErrorException class to turn all php errors into exceptions.

function handleError($errno, $errstr, $errfile, $errline, array $errcontext)
{
    // error was suppressed with the @-operator
    if (0 === error_reporting()) {
        return false;
    }

    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
}
set_error_handler('handleError');

try {
    dns_get_record();
}
catch (ErrorException $e) {
    // ...
}

Answer 3

If dns_get_record() fails, it should return FALSE, so you can suppress the warning with @ and then check the return value.