在 PHP 中检查 Not Null 和空字符串的语法

<?php
    // Define a simple string
    $sample_string = "I am a string";

    // Check if it's not null. We use PHP is_null
    // function, but we've added the negation
    // sign before it.
    if (!is_null($sample_string)) {
        echo "Your variable <b>" . $sample_string . "</b> is not null.";
    } else {
        echo "Your variable is null.";
    }
?>

Your variable <b>I am a string</b> is not null.

<?php
    $empty_string = "";
    $integer_zero = 0;
    $decimal_zero = 0.0;
    $string_zero = "0";
    $null_keyword = NULL;
    $boolean_false = FALSE;
    $array_with_no_data = [];
    $uninitialized_variable;

    if (empty($empty_string)) {
        echo "This message means the argument to function empty() was an empty string. <br />";
    }

    if (empty($integer_zero)) {
        echo $integer_zero . " is empty. <br />";
    }

    if (empty($decimal_zero)) {
        echo number_format($decimal_zero, 1) . " is empty. <br />";
    }

    if (empty($string_zero)) {
        echo $string_zero . " as a string is empty. <br />";
    }

    if (empty($null_keyword)) {
        echo "NULL is empty. <br />";
    }

    if (empty($boolean_false)) {
        echo"FALSE is empty. <br />";
    }

    if (empty($array_with_no_data)) {
        echo "Your array is empty. <br />";
    }

    if (empty($uninitialized_variable)) {
        echo "Yes, your uninitialized variable is empty.";
    }
?>

This message means the argument to function empty() was an empty string. <br />
0 is empty. <br />
0.0 is empty. <br />
0 as a string is empty. <br />
NULL is empty. <br />
FALSE is empty. <br />
Your array is empty. <br />
Yes, your uninitialized variable is empty.