What does "or" in php mean? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

PHP - and / or keywords

I saw several bits of PHP code using or in a way I was unfamiliar with. For example:

fopen($site,"r") or die("Unable to connect to $site");

Is this equal to this ||?

Why would you use this instead of a try catch block? What开发者_如何学Go will cause the program run the or die()?

---

It is for the most part, but...

The reason for the two different variations of "and" and "or" operators is that they operate at different precedences.

See http://php.net/manual/en/language.operators.logical.php

---

or is equal to || except that || has a higher presedense than or.

Reference:

http://www.php.net/manual/en/language.operators.precedence.php

---

or has an other precedence. The concrete statement is little trick with boolean operators. Like in a common if-test-expression the second part is only executed, if the first is evaluated to false. This means, if fopen() does not fail, die() is not touched at all.

However, try-catch only works with Exceptions, but fopen() doesnt throw any.

Today something like this is "not so good" style. Use exceptions instead of hard abortion

if (!($res = fopen($site, 'r'))) throw new Exception ("Reading of $site failed");

---

or die happens with the first command fails.

It is similar to a try catch, but this is more direct approach.

Note that this is a classical test:

fopen($site,"r") or die("Unable to connect to $site");

Only if fopen($site,"r") returns false, will the second half of the test be run: 'die('error')'.

Same is if(a || b); b is only run if a returns false.

Die in PHP is the same as exit(); http://www.php.net/manual/en/function.exit.php

Stops execution of the current script entirely, and prints out the error message.

---

Yes it equals ||

In this case it is explicitly stopping the execution of the page and printing that error message.