PHP Multi-line Comments – Syntax, Examples and Guide

PHP Multi-line Comments

PHP multi-line comments are used to write explanations, notes, and documentation across multiple lines of PHP code. They help developers describe complex logic, temporarily disable sections of code, and make programs easier to understand and maintain. Unlike single-line comments, which are generally used for short notes, multi-line comments are useful when a comment requires several lines of text.

PHP supports multi-line comments through the /* and */ symbols. Any text written between these symbols is treated as a comment and ignored by the PHP interpreter during program execution.

Understanding multi-line comments is an important part of learning PHP because clear comments improve code readability, simplify debugging, and support collaboration between developers.

What Are PHP Multi-line Comments?

A PHP multi-line comment is a block of text enclosed between an opening comment symbol (/*) and a closing comment symbol (*/). The comment can contain one line or multiple lines of text.

The opening symbol tells PHP where the comment begins, while the closing symbol indicates where the comment ends.

Syntax:

<?php
/*
This is a PHP multi-line comment.
It can contain several lines of text.
PHP ignores this comment during execution.
*/
echo "Hello, World!";
?>

Output:

Hello, World!

In this example, PHP ignores everything between /* and */ and executes the echo statement. The comment does not appear in the output.

How PHP Multi-line Comments Work

PHP multi-line comments work by marking a section of source code as non-executable commentary. When PHP processes the program, it recognizes the comment delimiters and excludes the enclosed text from normal code execution.

The opening delimiter, /*, begins the comment. The closing delimiter, */, ends it. Everything between these two delimiters is treated as comment text rather than executable PHP code.

For example:

<?php
/*
The following statement displays
a welcome message on the screen.
*/
echo "Welcome to PHP programming!";
?>

Output:

Welcome to PHP programming!

The comment explains the purpose of the statement without affecting its behavior.

A multi-line comment can also be written on a single line:

<?php
/* This is also a valid PHP multi-line comment. */
echo "Learning PHP";
?>

Although the comment occupies only one line, it uses the same block-comment syntax.

PHP Multi-line Comment Syntax

PHP uses two special symbols to create a multi-line comment.

The text between these symbols is ignored as a comment. The comment may include ordinary text, spaces, and line breaks.

Consider the following example:

<?php
/*
Program: Student Information
Purpose: Display student details.
Language: PHP
*/
echo "Student Name: Rahul";
?>

Output:

Student Name: Rahul

This example demonstrates how multi-line comments can provide useful information about a program before its executable statements begin.

Examples of PHP Multi-line Comments

Example 1: A Basic Multi-line Comment

A basic multi-line comment is useful when a developer wants to explain the purpose of a statement.

<?php
/*
This program displays
a simple greeting message.
*/
echo "Hello, PHP!";
?>

Output:

Hello, PHP!

The comment describes the program, but only the echo statement produces output.

Example 2: Commenting on a Calculation

Multi-line comments can explain mathematical operations or business calculations.

<?php
/*
Calculate the total price
of two products.
*/
$price1 = 100;
$price2 = 200;

$total = $price1 + $price2;

echo $total;
?>

Output:

300

The comment helps readers understand the calculation. PHP executes the variable assignments and addition normally.

Example 3: Using Multi-line Comments in Conditional Statements

Comments can explain why a condition is necessary.

<?php
/*
Check whether the student
has passed the examination.
*/
$marks = 75;

if ($marks >= 40) {
    echo "Pass";
} else {
    echo "Fail";
}
?>

Output:

Pass

The comment explains the purpose of the conditional statement without changing the result.

Example 4: Temporarily Disabling Code

Multi-line comments can be used to temporarily prevent a section of code from executing.

<?php
echo "First message";

/*
echo "This message is disabled.";
echo "This message is also disabled.";
*/

echo "Last message";
?>

Output:

First messageLast message

The two statements inside the comment block are not executed. This technique can be useful during development, but commented-out code should be removed when it is no longer needed.

Example 5: Writing Documentation for a Function

Multi-line comments are useful for documenting functions and explaining their expected behavior.

<?php
/*
Calculate the square of a number.

Parameter:
$num - The number to be squared.

Returns:
The square of the supplied number.
*/
function square($num) {
    return $num * $num;
}

echo square(5);
?>

Output:

25

This comment explains the function’s parameter and return value. For formal API documentation, PHP developers often use PHPDoc-style comments, which have additional conventions.

PHP Multi-line Comments vs Single-line Comments

PHP supports both single-line and multi-line comment styles. The main difference is how the comment is delimited and how developers typically use it.

Single-line comment example:

<?php
// Display a greeting
echo "Hello";
?>

Multi-line comment example:

<?php
/*
Display a greeting
to the user.
*/
echo "Hello";
?>

Both examples produce the same output:

Hello

Use single-line comments for brief notes and multi-line comments when a longer explanation or block of text is needed.

PHP Multi-line Comments vs PHPDoc Comments

PHP multi-line comments are also different from PHPDoc comments. Ordinary block comments begin with /*, whereas PHPDoc comments begin with /**.

PHPDoc comments follow conventions that allow documentation tools and development environments to identify information about functions, classes, properties, and parameters.

Ordinary multi-line comment:

<?php
/*
Returns the sum of two numbers.
*/
function add($a, $b) {
    return $a + $b;
}
?>

PHPDoc comment:

<?php
/**
 * Adds two numbers.
 *
 * @param int $a The first number.
 * @param int $b The second number.
 * @return int The sum of the numbers.
 */
function add(int $a, int $b): int {
    return $a + $b;
}
?>

The ordinary comment provides a general explanation. The PHPDoc comment uses structured tags such as @param and @return to describe the function’s interface.

For small scripts, ordinary comments are often sufficient. For reusable functions, classes, and libraries, PHPDoc can make documentation more consistent and useful.

Rules for Writing PHP Multi-line Comments

When writing multi-line comments in PHP, follow these basic rules:

1. Start with /*: Every block comment must begin with the opening delimiter.
2. Close with */: The closing delimiter ends the comment block.
3. Use comments to explain code: Describe the purpose of a statement or the reasoning behind a complicated operation.
4. Avoid unnecessary comments: Comments should add information rather than repeat what the code already makes obvious.
5. Keep comments accurate: Update comments whenever the associated code changes.
6. Do not use ordinary block comments as nested comments: PHP block comments do not support nesting.
7. Avoid commenting out large sections permanently: Remove obsolete code instead of leaving it commented out indefinitely.
8. Do not place sensitive information in comments: Source code may be shared or published, so comments should never contain passwords, API keys, or private credentials.

These practices help maintain clean, understandable, and secure PHP programs.

Important Limitation: Nested Multi-line Comments

PHP does not support nested block comments. This means that placing another /* ... */ comment inside an existing block comment can cause the outer comment to end earlier than expected.

For example, the following code is problematic:

<?php
/*
This is the outer comment.

/*
This is an attempted inner comment.
*/

echo "Hello";
*/
?>

The first */ closes the original block comment. The remaining text may then be interpreted as PHP code, potentially resulting in a syntax error.

To avoid this problem, do not place ordinary block-comment delimiters inside another block comment. If you need to temporarily disable code containing block comments, consider using another commenting approach or carefully restructure the code.

Advantages of PHP Multi-line Comments

Multi-line comments offer several benefits in PHP development.

Improved readability: They explain complex sections of code and help readers understand a program’s purpose.

Easier maintenance: Developers can understand the reasoning behind existing code when fixing bugs or adding features.

Better teamwork: Comments provide context for other developers working on the same project.

Simplified testing: Developers can temporarily disable a group of statements while investigating a problem, provided the code is commented out safely.

Better documentation: Block comments can describe program modules, functions, algorithms, and important implementation details.

However, comments should support well-written code rather than replace meaningful variable names, simple logic, and appropriate documentation.

Common Mistakes When Using PHP Multi-line Comments

Forgetting the Closing Delimiter

If a block comment is not properly closed, PHP may treat subsequent code as part of the comment or report a syntax error, depending on the surrounding code.

Incorrect:

<?php
/*
This comment is not closed.
echo "Hello";
?>

Correct:

<?php
/*
This comment is properly closed.
*/
echo "Hello";
?>

Using the Wrong Closing Symbol

The closing delimiter is */, not /*. Reversing the symbols does not close a comment block correctly.

Writing Comments That Contradict the Code

A comment that describes outdated behavior can mislead developers. Always review comments when modifying the code they describe.

Assuming Comments Produce Output

Text inside a comment block is not displayed in the browser or command-line output. Use statements such as echo or print when you need to display text.

Confusing Comments With PHPDoc

An ordinary block comment is not automatically a structured PHPDoc comment. Use /** ... */ and appropriate documentation tags when generating formal documentation.

Best Practices for PHP Multi-line Comments

Professional PHP code benefits from comments that are short, accurate, and meaningful.

• Explain why a complicated operation is necessary instead of simply repeating what the code does.
• Use complete sentences when writing longer explanations.
• Separate different ideas into readable paragraphs or lines.
• Document assumptions, limitations, and important business rules.
• Use PHPDoc for functions, classes, and other reusable components when structured documentation is appropriate.
• Remove temporary debugging comments and obsolete code before releasing an application.
• Remember that comments do not improve security or validate input; implement the necessary security controls in executable code.

A well-placed comment can save time during debugging and maintenance. Too many unnecessary comments, however, can make code harder to read.

Frequently Asked Questions (FAQs)

1. What is a multi-line comment in PHP?

A multi-line comment is a section of source code enclosed between /* and */. It allows developers to write explanations across multiple lines without executing the comment text.

2. What is the syntax of a PHP multi-line comment?

The syntax is:

/*
Your comment text goes here.
It can contain multiple lines.
*/

3. Are PHP multi-line comments executed?

No. PHP ignores the contents of a comment block during normal code execution. Statements written entirely inside the comment are not executed.

4. Can PHP multi-line comments contain multiple lines?

Yes. A single block comment can contain several lines of text, explanations, or commented-out code.

5. What is the difference between // and /* */ in PHP?

The // symbol starts a single-line comment, while /* and */ mark the beginning and end of a block comment. Both are ignored by PHP during normal execution.

6. Can PHP multi-line comments be nested?

No. PHP does not support nested ordinary block comments. An inner */ can close the outer comment unexpectedly.

7. What is the difference between /* */ and /** */?

The /* */ syntax is used for ordinary block comments. The /** */ syntax is commonly used for PHPDoc documentation, which supports structured tags for describing functions, parameters, return values, and other code elements.

8. Can multi-line comments be used to disable PHP code?

Yes. Enclosing code within a block comment can temporarily prevent it from executing. However, the code must not contain conflicting block-comment delimiters, and temporary commented-out code should be removed when it is no longer needed.

9. Do PHP multi-line comments appear in browser output?

No. The comment text itself does not appear in normal PHP output. Only executable statements, such as echo, produce the displayed text.

10. Why are multi-line comments important in PHP?

They improve code readability, explain complex logic, support maintenance, and help developers communicate the purpose of program sections.

Conclusion

PHP multi-line comments are a simple but useful feature for documenting and maintaining PHP programs. By using /* to begin a comment and */ to end it, developers can write explanations across multiple lines without affecting normal program execution.

Multi-line comments are especially helpful for documenting complex calculations, describing conditional logic, explaining functions, and temporarily disabling small sections of code. For formal documentation, PHPDoc comments provide a more structured alternative.

Using comments thoughtfully makes PHP code easier to understand, maintain, and share with other developers.