default variable value

[Anon]

If a variable isn't defined, what does it's value default to?

so for example, i have a url below:

form.php?t=4

In the above url there is no "g" in the querystring BUT what would it's value be if I wanted to compare it in a if statement?

-Surojit

[Anon]

Hi,

If you treat $g as a number, i guess it would be $g == 0.
If you treat it like a string, strlen($g) == 0.

Hope this helps you out, good luck.

[[deleted]]

Wrong I'm affraid.

an Undefined variable is exactly that: undefined.

It has no value, it's illegal to use, bad naughty bad go stand in a corner and be ashamed bad.

A) this should never happen because your program should check EVERY variable when it's first used to see if it's defined:
if (!isset($variable))
{
// variable not defined, give it a default value.
};

😎 PHP can't deal with something undefined, which means that allmost every function you put an 'undefined' into will fail and return 'FALSE'.
This means that things like this will work if $g is not defined:

if (!$g)
{
// $g was not supplied
};

But this is EXTEREMELY BAD PRACTICE.
And why? because this just checks if $g!=0.
PHP can't handle 'undefined', so it treats $g as if it where FALSE, and then it works.
But in PHP FALSE=0, so if $g=0 this function would also work. et presto: doodie hit's the fan.

Tip: allways start your scripts with:
error_reporting(E_ALL);

that will tell you everything you are doing wrong.
A good script is one that has zero errors and zero warnings.

[rolfnilsen]

I know, am a bad person spreading my bad habits like this :-)

I will try not to do it again, and I dont dispute what you say.
You are absolutely right !

I guess what saves me from trouble is PHP's way of handling
types ?

(I sure hope it's a long time until the next code review :-)

[Anon]

I think isset() will do the trick. However, are you saying this is bad practice?

-Surojit

[[deleted]]

Using isset() to check if a var is set is GOOD practice.
Using if () to see if a var is set is BAD practice.

Good: if(!isset($var)) { echo 'not set'; };
Bad: if (!$var) { echo 'not set'; };