The equality comparison operator in PHP is an ‘=’? What’s the assignment operator?

Or are you deliberately assigning $bar to $foo?

In C a boolean expression is False if it evaluates to 0; otherwise I believe it is treated as True (non-zero, usually 1 (I don’t remember if the programmer has to specify the non-zero value).

NULL is the value to which pointers are assigned to mean it has no memory assigned to it.

A string var has to be compared specifically to an empty string to test if it has any characters assigned to it.

In C++ I’m not sure how it all works …

In Perl, I think Null is a specific value meaning ‘undetermined’; 0 and FALSE are treated as FALSE; an empty string I think also evaluates to False. Casting the integer 0 to a string … I’m not sure. It looks like in PHP it returns an empty string and not a character value for the integer ‘0′.

Does an empty string evaluate to False in PHP?

= is the assignment operator. == is the comparison operator. Syntax is the same as C. Which is why I was confused, because I thought the assignment operator always evaluated TRUE unless you tried to assign something to NULL. Actually, now that I think about it, assigning something to NULL should also return TRUE in C, right?

Unlike C, in PHP you don’t have to declare variables. It’s a lot easier for the lazy coder that way. So in the above cases, $foo is never declared, and could be anything (char, int, boolean). In PHP if you assign, for example, an int ($foo) to a char/string ($bar), then $foo becomes a char/string.

For example, the following is completely valid:

$foo = (int) 0;
$bar = (string) ‘bar’;
$foo = bar;
echo $foo; // returns ‘bar’

BTW, the reason I bring this up is because I saw in someone’s script the use of something like,

if ($foo = db_query('SELECT field FROM table'))

as a shortcut for

if (db_query('SELECT field FROM table'))
   $foo = db_query('SELECT field FROM table');


where db_query is a function which returns NULL (or empty array?) if no values found. At first when I saw this I thought it was a typo (= instead of ==), but then I realized it wasn’t and, following up on it, discovered the weird results described in my post.

Hmmm … I think the value NULL evaluates to False in C as well, unless you make an explicit comparison (e.g. if (i == NULL) { … } ) and the resultant value is the value of the expression (if i is a pointer variable and had been assigned to null prior to the comparison, the comparison should evaluate to True). But if the comparison is simply if (i) { … } with the same conditions, it would evaluate to False, I believe.

Ya, that’s what I originally thought too. So NULL is one case where PHP and C are the same. But the “FALSE” and “0″ cases are just plain weird in PHP. :p