When should I use a bitwise operator?

 

I read the following Stack Overflow questions, and I understand the differences between bitwise and logical.

  • Difference between & and && in PHP

  • Reference - What does this symbol mean in PHP?

    • However, none of them explains when I should use bitwise or logical.

    When should I use bitwise operators rather than logical ones and vice versa?

    In which situation do I need to compare bit by bit?

    I am not asking about the differences, but I am asking the situation when you need to use bitwise operators.

    Bitwise | and & and logical || and && are totally different.

    Bitwise operators perform operations on the bits of two numbers and return the result. That means it's not a yes or no thing. If they're being used in conditional statements, they're often used as part of logical comparisons. For example: 

    if ($x & 2 == 2) {
    // The 2^1 bit is set in the number $x
}

    Logical operators compare two (or more) conditions/expressions and return true or false. You use them most commonly in conditional statements, like if and while . For example: 

    if ($either_this || $or_this) {
    // Either expression was true
}

    Bitwise is useful for things in PHP just like anything else.

    How about a value that can have multiple states turned on at the same time (perhaps permissions)? 

    <?php

# must double them like this for it to work.
const STATE_FOO = 1;
const STATE_BAR = 2;
const STATE_FEZ = 4;
const STATE_BAZ = 8;

# set state to foo and fez
$state = STATE_FOO | STATE_FEZ;

echo "What's the value: $staten";
echo "Is foo state on? ".(bool)($state & STATE_FOO)."n";
echo "Is bar state on? ".(bool)($state & STATE_BAR)."n";
echo "Is fez state on? ".(bool)($state & STATE_FEZ)."n";
echo "Is baz state on? ".(bool)($state & STATE_BAZ)."n";
echo "Is foo and fez state on? ".($state == (STATE_FOO | STATE_FEZ))."n";

    In most cases, you'll probably want to use logical operators. They're used for combining logical conditions, generally to control program flow, eg ($isAlive && $wantsToEat) .

    Bitwise operators are used when you want to perform operations on a bit-by-bit basis on the underlying binary representations of integers. eg (5 & 3) == 7 . As others have suggested, there's usually not a lot of call for this in the sort of application that tends to get written in PHP (although there is in lower-level languages, like C).

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