What is the correct way to check if bit field is turn on in php

问题

What is the correct way to check if bit field is turn on - (in php) ?

I want to check a bit field that come from db(mysql) if is turn on or not.

is this is the correct way ?

if($bit & 1)

Are there other ways ?

I see somebody code that using ord() function , it is correct ?

like if(ord($bit) == 1)

回答1:

Use

if( $bit & (1 << $n) ) {
  // do something
}

Where $n is the n-th bit to get minus one (for instance, $n=0 to get the least significant bit)

回答2:

It's a bit late but might be usefull for future visitors to this question. I've made myself a little function that returns all bits that are active in a certain flag.

/**
 * Shows all active bits
 *
 * @param int $flag
 * @return array
 */
function bits($flag)
{
    $setBits = array();
    for ($i = 1; $i <= 32; $i++) {
        if ($flag & (1 << $i)) {
            $setBits[] = (1 << $i);
        }
    }

    // Sort array to order the bits
    sort($setBits);

    return $setBits;
}

echo "<pre>";
var_dump(bits(63));
echo "</pre>";

回答3:

I use

if (($flag & 0b010) == 0b010) {
  // here we know that the second bit (dec 2) is set in $flag
}

回答4:

Yes, if($bit & 1) is the correct way to check, according to the PHP manual.

An alternative could be to do the check in your MySQL query.

回答5:

To get the correct bit, use this syntax:

$bit & (1 << $n)

Where $n is to get the (n+1)-th least significant bit. So $n=0 will get you the first least significant bit.

来源：https://stackoverflow.com/questions/3511709/what-is-the-correct-way-to-check-if-bit-field-is-turn-on-in-php