How to correctly determine whether the return value of stripos is false?

In PHP, the stripos() function is used to find where a string first appears in another string (case insensitive). This function is often used when processing string-related logic, such as determining whether a keyword exists in a given content.

However, due to the return value characteristic of stripos() , many developers are prone to stumble when making judgments, especially for processing the return value of 0 . This article will analyze this issue in detail and give a correct way of judgment.

1. Basic usage of the stripos() function

 $haystack = "Welcome to m66.net!";
$needle = "welcome";

$pos = stripos($haystack, $needle);

In the example above, stripos() will return 0 because "welcome" appears at the beginning of the target string (though case is different, stripos() is case-insensitive).

2. Common misunderstandings: Use if directly to judge

Many beginners will write this way:

 if (stripos($haystack, $needle)) {
    echo "Found the keyword";
} else {
    echo "Keywords do not exist";
}

The problem with this code is that if the keyword appears at the beginning of the string (position is 0), if judgment will treat 0 as false , and the else branch is incorrectly executed .

3. Correct way of judgment: all equal to false

 $pos = stripos($haystack, $needle);
if ($pos !== false) {
    echo "Found the keyword，Location is：$pos";
} else {
    echo "Keywords do not exist";
}

Using the writing method that is equal to ( !== false ) can accurately distinguish whether the function returns 0 or false , thereby avoiding logical errors.

4. Examples of application scenarios

For example, we want to detect whether the comments submitted by a user contain certain sensitive words and give a reminder: