difference between & and && in PHP

Question

Hi,

I am confused with & and &&. I have two PHP books. One says that they are same, but the another says they are different. I thought they are same as well.

Aren't they same???

Answer 1

& is bitwise AND. See Bitwise Operators. Assuming you do 14 & 7:

    14 = 1110
     7 = 0111
    ---------
14 & 7 = 0110 = 6

&& is logical AND. See Logical Operators. Consider this truth table:

 $a     $b     $a && $b
false  false    false
false  true     false
true   false    false
true   true     true

Answer 2

As the others are saying, single & is bit-wise, it basically converts the left-hand value into its bits representation, and the right hand side into bits representation as well, then performs logical AND between them and outputs the result, while double && is either true or false, (in some languages 0 or 1) if both left and right side are true (or non-zero). i'd also add that this is not just in php, it is like that in many many other languages as well like C, Java, Ruby etc.

Answer 3

The other answers are correct, but incomplete. A key feature of logical AND is that it short-circuits, meaning the second operand is only evaluated if necessary. The PHP manual gives the following example to illustrate:

$a = (false && foo());

foo will never be called, since the result is known after evaluating false. On the other hand with

$a = (false & foo());

foo will be called (also, the result is 0 rather than false).