Double check of variables.

[opt_inf_env]

Hello,

In some examples of a PHP implementation I saw the following:
if ( isset(x) and x==12)
I do not understand what for before to check whether some variable has
some value one need to check whether this variable is set. If the
second condition is true than the first one is also true, isn't?

[Shelly]

<op*********@yahoo.com> wrote in message
news:11*********************@g49g2000cwa.googlegro ups.com...

Hello,

In some examples of a PHP implementation I saw the following:
if ( isset(x) and x==12)
I do not understand what for before to check whether some variable has
some value one need to check whether this variable is set. If the
second condition is true than the first one is also true, isn't?

The order of checking here is the same as in C, C++, Java, etc. It checks
the first condition. If that fails, it does NOT check the second condition.
If you were to check the second condtion only, then it might cause an error
condition that produces undesirable results. In the case you cite, that
probably won't happen. It is generally used best when you might have a
pointer off into never-never land. So, it is good programming practice to
alway be CERTAIN that your variable being tested actually exists before
testing its value.

Shelly

[pfrank26]

The reason for isset check is that without it, if x isn't set, PHP will
generate a warning on some systems.

[R.Lange]

op*********@yahoo.com wrote:

Hello,

In some examples of a PHP implementation I saw the following:
if ( isset(x) and x==12)
I do not understand what for before to check whether some variable has
some value one need to check whether this variable is set. If the
second condition is true than the first one is also true, isn't?

Yes, but the problem occurs when the variable *isn't* set.

<?php
//$x = 12;
if ($x == 12) {
echo 'The variable $x is equal to 12.';
}
?>

The above code will give you the following:
"Notice: Undefined variable: x in [file] on line [line]"

It's not fatal, so the script will keep going, but it's generally not a
good idea to just ignore things like that.

- Ryan