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    is_null

    (PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

    is_null — 変数が null かどうか調べる

    説明

    is_null(mixed $value): bool

    指定した変数が null かどうかを調べます。

    パラメータ

    value

    評価する変数。

    戻り値

    value が null の場合に true、 それ以外の場合に false を返します。

    例

    例1 is_null() の例

    <?php

    error_reporting    (E_ALL);

    $foo = NULL;
    var_dump(is_null($inexistent), is_null($foo));

    ?>
    Notice: Undefined variable: inexistent in ...
bool(true)
bool(true)

    参考

    • null 型
    • isset() - 変数が宣言されていること、そして null とは異なることを検査する
    • is_bool() - 変数が boolean であるかを調べる
    • is_numeric() - 変数が数字または数値形式の文字列であるかを調べる
    • is_float() - 変数の型が float かどうか調べる
    • is_int() - 変数が整数型かどうかを検査する
    • is_string() - 変数の型が文字列かどうかを調べる
    • is_object() - 変数がオブジェクトかどうかを検査する
    • is_array() - 変数が配列かどうかを検査する

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    User Contributed Notes 5 notes

    up
    337
    Malfist
    16 years ago
    Micro optimization isn't worth it.

    You had to do it ten million times to notice a difference, a little more than 2 seconds

    $a===NULL; Took: 1.2424390316s
    is_null($a); Took: 3.70693397522s

    difference = 2.46449494362
    difference/10,000,000 = 0.000000246449494362

    The execution time difference between ===NULL and is_null is less than 250 nanoseconds. Go optimize something that matters.
    up
    166
    george at fauxpanels dot com
    16 years ago
    See how php parses different values. $var is the variable.

    $var = NULL "" 0 "0" 1

    strlen($var) = 0 0 1 1 1
    is_null($var) = TRUE FALSE FALSE FALSE FALSE
    $var == "" = TRUE TRUE TRUE FALSE FALSE
    !$var = TRUE TRUE TRUE TRUE FALSE
    !is_null($var) = FALSE TRUE TRUE TRUE TRUE
    $var != "" = FALSE FALSE FALSE TRUE TRUE
    $var = FALSE FALSE FALSE FALSE TRUE

    Peace!
    up
    89
    contact dot 01834e2c at renegade334 dot me dot uk
    9 years ago
    In PHP 7 (phpng), is_null is actually marginally faster than ===, although the performance difference between the two is far smaller.

    PHP 5.5.9
    is_null - float(2.2381200790405)
    === - float(1.0024659633636)
    === faster by ~100ns per call

    PHP 7.0.0-dev (built: May 19 2015 10:16:06)
    is_null - float(1.4121870994568)
    === - float(1.4577329158783)
    is_null faster by ~5ns per call
    up
    23
    ahamilton9
    2 years ago
    A quick test in 2022 on PHP 8.1 confirms there is still no need to micro-optimize NULL checks:

    <?php

    // Comparison Operator
    $before = microtime(true);
    $var = null;
    for (    $i=0 ; $i<1000000000 ; $i++) {
    if(    $var === null) {}
    }
    $after = microtime(true);
    echo     ' ===: ' . ($after - $before) . " seconds\n";

    // Function
    $before = microtime(true);
    $var = null;
    for (    $i=0 ; $i<1000000000 ; $i++) {
    if(    is_null($var)) {}
    }
    $after = microtime(true);
    echo     'is_null: ' . ($after - $before) . " seconds\n";

    // ===: 4.1487579345703 seconds
    // is_null: 4.1316878795624 seconds
    up
    16
    ai dot unstmann at combase dot de
    16 years ago
    For what I realized is that is_null($var) returns exactly the opposite of isset($var) , except that is_null($var) throws a notice if $var hasn't been set yet.

    the following will prove that:

    <?php

    $quirks     = array(null, true, false, 0, 1, '', "\0", "unset");

    foreach(    $quirks as $var) {
    if (    $var === "unset") unset($var);

    echo     is_null($var) ? 1 : 0;
    echo isset(    $var) ? 1 : 0;
    echo     "\n";
    }

    ?>

    this will print out something like:

    10 // null
    01 // true
    01 // false
    01 // 0
    01 // 1
    01 // ''
    01 // "\0"
    Notice: Undefined variable: var in /srv/www/htdocs/sandbox/null/nulltest.php on line 8
    10 // (unset)

    For the major quirky types/values is_null($var) obviously always returns the opposite of isset($var), and the notice clearly points out the faulty line with the is_null() statement. You might want to examine the return value of those functions in detail, but since both are specified to return boolean types there should be no doubt.

    A second look into the PHP specs tells that is_null() checks whether a value is null or not. So, you may pass any VALUE to it, eg. the result of a function.
    isset() on the other hand is supposed to check for a VARIABLE's existence, which makes it a language construct rather than a function. Its sole porpuse lies in that checking. Passing anything else will result in an error.

    Knowing that, allows us to draw the following unlikely conclusion:

    isset() as a language construct is way faster, more reliable and powerful than is_null() and should be prefered over is_null(), except for when you're directly passing a function's result, which is considered bad programming practice anyways.
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