PHP’s strpos() is a handy function used to find the position of a substring (the “needle”) inside another string (the “haystack”). It’s super useful for input validation, text processing, and more.

🧠 Syntax

strpos(string $haystack, string $needle, int $offset = 0)
  • $haystack: The full string you’re searching in.
  • $needle: The part you’re looking for.
  • $offset (optional): Where to start the search from.

🔁 What It Returns

  • If found → returns the position (starting at 0).
  • If not → returns false.

✅ Always use !== false for checks. Why? Because a return value of 0 means the match is at the very start — and 0 == false would be misleading.

📌 Example

$text = "Hello, world!";
$search = "world";
$pos = strpos($text, $search);

if ($pos !== false) {
  echo "Found at position: $pos";
} else {
  echo "Not found.";
}

Output: Found at position: 7

⚠️ Things to Note

  • Case-sensitive: "World" ≠ "world".
  • Binary-safe.
  • Use strict comparison to avoid false positives.

💡 Use Cases

  • Checking for banned words in user input
  • Parsing logs or CSV files
  • Extracting data
  • Cleaning up messy strings

🧪 Quick Quiz

1. What does strpos() return if the needle isn’t found? a) 0 b) “not found” c) false d) error message

2. What’s the output?

$text = "This is a sample string.";
$search = "sample";
echo strpos($text, $search);

✅ Wrap-Up

strpos() is small but mighty. Mastering it helps you write smarter string-handling code in PHP. Try it out in your next form validation or data parser!

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