PHP function introduction—empty(): Check whether the variable is empty

PHP function introduction—empty(): Check whether a variable is empty

In PHP programming, it is often necessary to judge variables. It is a common requirement to judge whether a variable is empty. PHP's built-in empty() function is used to check whether the variable is empty. This article will introduce the usage of the empty() function and provide some practical code examples.

The usage of the empty() function is very simple. It accepts one parameter and returns a Boolean value. The empty() function returns true when the value of the parameter is one of the following situations, otherwise it returns false:

1. If the value of the variable is 0 or the string "0", it is considered empty.
2. If the value of the variable is false or null, it is considered empty.
3. If the value of a variable is an empty array (array()) or an empty object with no elements, it is considered empty.
4. If the variable is not set at all, it is considered empty.

The following is a sample code showing the usage of the empty() function:

<?php
$var1 = '';
$var2 = 0;
$var3 = false;
$var4 = null;
$var5 = array();
$var6; // not set

echo 'var1 is empty: ' . (empty($var1) ? 'true' : 'false') . '<br>';
echo 'var2 is empty: ' . (empty($var2) ? 'true' : 'false') . '<br>';
echo 'var3 is empty: ' . (empty($var3) ? 'true' : 'false') . '<br>';
echo 'var4 is empty: ' . (empty($var4) ? 'true' : 'false') . '<br>';
echo 'var5 is empty: ' . (empty($var5) ? 'true' : 'false') . '<br>';
echo 'var6 is empty: ' . (empty($var6) ? 'true' : 'false') . '<br>';
?>

Running the above code will output the following results:

var1 is empty: true
var2 is empty: true
var3 is empty: true
var4 is empty: true
var5 is empty: true
var6 is empty: true

In actual programming In , we often need to judge whether a variable is empty to make logical judgments. For example, we can use the empty() function to check whether the form data entered by the user is empty to ensure the validity of the data.

<?php
if (empty($_POST['username'])) {
    echo '请输入用户名';
} else {
    // 其他逻辑处理
}
?>

In the above code snippet, we use the empty() function to check whether the user name entered by the user is empty. If it is empty, prompt information will be output, otherwise other logical processing will be performed.

It should be noted that the empty() function can only be used for variable checking and cannot be used to directly determine the truth or falsehood of constants or expressions. For example, if we need to determine whether a constant is empty, we should use the isset() function. If you need to determine whether an expression is true or false, you should use an if statement.

In short, the empty() function is a very practical function in PHP, which allows us to conveniently check whether a variable is empty. In actual programming, we often need to use the empty() function to perform form data verification, logical judgment, etc. I hope that the introduction and sample code of this article can help readers better understand and use the empty() function.

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