Is_null ($var)和($var = = null)之间的区别是什么？

Both are exactly same, I use is_null because it makes my code more readable

I would use the built in PHP function over the operator comparison every time.

Provided the variable is initialized (which you did indicate - though I'm not 100% sure if this matters in this context or not. Both solutions might throw a warning if the variable wasn't defined), they are functionally the same. I presume === would be marginally faster though as it removes the overhead of a function call.

It really depends on how you look at your condition.

=== is for a strict data comparison. NULL has only one 'value', so this works for comparing against NULL (which is a PHP constant of the null 'value')

is_null is checking that the variable is of the NULL data type.

It's up to you which you choose, really.

is_null($var) is about 14 times slower than $var===null... 37.8 ms vs. 2.6 ms.

But actually I don't know why.

I've just run a quick benchmark, testing a million iterations of each. is_null took 8 seconds to complete; === null took 1.

So a call to is_null is 0.000007s slower than a call to === on my computer.

I'd find something more useful to optimise.

My code:

<?php


$start = time();
$var = null;


for ($i = 1000000; $i--; ) {
is_null($var);
}


echo time() - $start;


$start = time();


for ($i = 1000000; $i--; ) {
$var === null;
}


echo time() - $start;

If it seems redundant for php to have so many is_foo() type functions, when you can just use a standard comparison operators, consider programatically called functions.

$arrayOfNullValues = array_filter($myArray, 'is_null');

empty() and isset() do not trigger a PHP warning if their parameter is an undefined variable. In most cases, such a warning is desirable to pinpoint the bugs. So only use the functions if you believe your variable can be legitimately undefined. It normally happens with an array index.

✅ is true

❌ is false

        |  isset   | is_null | === null | == null | empty   |
|-------|----------|---------|----------|---------|---------|
| unset |    ❌   |    ✅   |    ✅    |    ✅  |    ✅   |
|  null |    ❌   |    ✅   |    ✅    |    ✅  |    ✅   |
|  true |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
| false |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|     0 |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|     1 |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
|    \0 |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
|    "" |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|    [] |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |

Summary:🔸♦️🔸

• empty is equivalent to == null
• is_null is equivalent to === null
• isset is inverse of is_null and === null

One thing people often forget to mention in this discussion is that if you are all about strict type checking, is_null will help you to never make a typo in your comparison operators (== vs ===).