Difference between if(isset($var)) and if($var) [duplicate]

Question

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Whats the difference between if(!Variable) and if(isset($variable)) ?

In Facebooks php API example they use if($var){ //do something }else{ //do something else} whick got me thinking about the difference of if($var) and if(isset($var)). The first sure looks neater but can I surely use it?

Answer 1

Using

if ($var)

You'll test if $var contains a value that's not false -- 1 is true, 123 is too, ...

For more informations about what is considered as true or false, you should take a look at Converting to Boolean.

Using isset(), you'll test if a variable has been set -- i.e. if any not-null value has been written to it.

Answer 2

The difference is that the isset will be true for any variable that has been declared/initalized to anything (besides null). the if($var) is true for all values of var OTHER THAN those that evaluate to false (0, '', null, false, etc).

So the difference is for values that are not null, but still evaluate to false: 0, '' (empty string), false, empty array, etc.

Try this:

$var = '';  //or equivalently 0, false, ''

if(isset($var)) echo 'a';
if($var) echo 'b';