Under the latest CVS, the following script fails (ftruncate() returns an error and doesn't truncate the file) but under PHP 4.1.2, it works fine:

<?php

if (! $fp = fopen('test','r+')) {
    die("Can't open test");
}

if (! ftruncate($fp,0)) {
    die("Can't truncate");

}

fclose($fp);

?>

(The file "test" exists and has some text in it.)

I get the same results whether the mode passed to fopen() is "r", "r+", "a", or "a+" (with "w" or "w+", the call to ftruncate() still fails, but the file is truncated due to the nature of the "w" fopen mode).