❓ PHP Null Coalescing Operator (??) – Complete Guide with Examples

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🧲 Introduction – Why Null Coalescing Matters

When handling variables like $_GET, $_POST, or config options, you’re often unsure if a value exists or is null. Enter the null coalescing operator (??), which helps you safely access variables with a fallback default — all in one line.

🎯 In this guide, you’ll learn:

• What the null coalescing operator is
• How it compares to isset() and ternary ?:
• Practical use cases with examples
• Common pitfalls and performance benefits

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📘 What is the Null Coalescing Operator in PHP?

The ?? operator returns the first operand if it exists and is not null; otherwise, it returns the second operand.

✅ It’s a shorthand for:

isset($var) ? $var : 'default';

But written as:

$var ?? 'default';

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🧪 Syntax

$result = $value ?? 'default';

✅ Returns:

• $value if it exists and is not null
• 'default' otherwise

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🔍 Practical Examples

✅ 1. Fallback for Optional Input

$name = $_GET['name'] ?? 'Guest';
echo "Welcome, $name!";

📘 Explanation:
If $_GET['name'] exists → use it.
Else → default to "Guest".

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✅ 2. Shorter Alternative to isset()

$color = isset($_POST['color']) ? $_POST['color'] : 'blue';

Becomes:

$color = $_POST['color'] ?? 'blue';

🧠 Cleaner and easier to read!

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✅ 3. Chained Fallbacks

$username = $input ?? $cookie ?? $default ?? 'Anonymous';

📘 Explanation:
Use $input if available, else $cookie, then $default, finally 'Anonymous'.

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✅ 4. Null vs Empty

$var = null;
echo $var ?? 'fallback';  // fallback

$var = 0;
echo $var ?? 'fallback';  // 0

📘 Explanation:
Only null triggers fallback. 0, false, "", etc. are treated as valid.

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🧠 Best Practices

• ✅ Use ?? when you’re unsure a variable is set
• ✅ Chain ?? for multiple fallbacks
• ❌ Don’t confuse ?? with ||, which checks truthiness
• ✅ Prefer ?? over isset() + ternary for readability and performance

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⚠️ PHP Version Compatibility

Feature	PHP Version
Null Coalescing (??)	PHP 7.0+
Chained Null Coalescing	PHP 7.0+

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📌 Summary – Recap & Next Steps

The null coalescing operator (??) makes defaulting logic cleaner and safer. It helps eliminate errors like “undefined index” and reduces the need for verbose isset() checks.

🔍 Key Takeaways:

• Use ?? for default fallbacks when variables might be unset or null
• Works great with $_GET, $_POST, config arrays, or function parameters
• Cleaner and safer than older ternary patterns

⚙️ Real-World Relevance:
Used in form handling, dynamic configuration, API requests, and routing systems.

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❓ Frequently Asked Questions (FAQs)

❓ What does the ?? operator do in PHP?
✅ It checks if the variable exists and is not null — if not, it returns the fallback value.

❓ Is ?? the same as isset($x) ? $x : $default?
✅ Yes, but shorter and cleaner.

❓ Does ?? consider 0, false, or “” as null?
❌ No. Only null triggers fallback. 0, false, and empty string are valid.

❓ Can I chain multiple ?? operators?
✅ Yes. PHP evaluates from left to right until it finds a value that is not null.

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