flock function

i saw this code in a book and i didn t understand why flock is being used . and when we use it isn t it like this  
(flock($file1, LOCK_EX)) ???

<?php
$idfile=fopen("connex.txt","a");
$date=time();;
flock($idfile,2);
fwrite($idfile,$date);
flock($idfile,3);
fclose($idfile);
//Lecture des données
$idfile=fopen("connex.txt","r");
flock($idfile,1);
hamza somaiAsked:
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Julian HansenCommented:
LOCK_SH
LOCK_EX
LOCH_UN
Are defines that have values 1,2 and 3 - so while it makes more sense to use LOCK_EX and more readable - it is also possible to use the numbers. Personally I don't see why they did it that way but it is still valid.

As to why - I imagine it is part of an example to demonstrate how file locking works. First create an exclusive lock on the file to append to it, release the lock and then acquire a shared lock on the file to read it.
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Ray PaseurCommented:
I would always use the LOCK_xx notation.  It's easier to read and understand.  You might want to check the date and popularity of that book.  Using a number when you should be using a named constant seems like a code smell to me!
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