How exactly does if($variable) work? [duplicate]

Question

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Regarding if statements in PHP

In PHP scripts - what does an if statement like this check for?

<?php if($variable){ // code to be executed } ?>   

I've seen it used in scripts several times, and now I really want to know what it "looks for". It's not missing anything; it's just a plain variable inside an if statement... I couldn't find any results about this, anywhere, so obviously I'll look stupid posting this.

Answer 1

The construct if ($variable) tests to see if $variable evaluates to any "truthy" value. It can be a boolean TRUE, or a non-empty, non-NULL value, or non-zero number. Have a look at the list of boolean evaluations in the PHP docs.

From the PHP documentation:

var_dump((bool) "");        // bool(false) var_dump((bool) 1);         // bool(true) var_dump((bool) -2);        // bool(true) var_dump((bool) "foo");     // bool(true) var_dump((bool) 2.3e5);     // bool(true) var_dump((bool) array(12)); // bool(true) var_dump((bool) array());   // bool(false) var_dump((bool) "false");   // bool(true) 

Note however that if ($variable) is not appropriate to use when testing if a variable or array key has been initialized. If it the variable or array key does not yet exist, this would result in an E_NOTICE Undefined variable $variable.

Answer 2

If converts $variable to a boolean, and acts according to the result of that conversion.

See the boolean docs for further information.

To explicitly convert a value to boolean, use the (bool) or (boolean) casts. However, in most cases the cast is unnecessary, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.