What are some common pitfalls when using strpos in PHP?

One common pitfall when using strpos in PHP is not checking for strict comparison (===) when evaluating the result. This is because strpos can return 0 if the substring is found at the beginning of the string, which can be falsely interpreted as false in a loose comparison. To avoid this, always use strict comparison when checking the result of strpos. 

// Incorrect way to check for substring existence
if (strpos($haystack, $needle)) {
    echo "Substring found!";
} else {
    echo "Substring not found!";
}

// Correct way to check for substring existence
if (strpos($haystack, $needle) !== false) {
    echo "Substring found!";
} else {
    echo "Substring not found!";
}

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