PHP highlight_string() Function: Usage and Examples

Use highlight_string() when you need to produces HTML-formatted syntax highlighting for PHP source code in a PHP application. The examples below show the actual operation and its limitations.

What Is highlight_string() in PHP?

Produces HTML-formatted syntax highlighting for PHP source code. The exact signature supported by your installation depends on its PHP version and enabled extensions.

Its syntax is:

highlight_string(string $string, bool $return = ...): string|true

Parameters and return value: The parameter types, optional arguments, references, and return type are shown in the signature above. Optional parameters are marked with an ellipsis in this reference signature.

Example 1: Basic Usage

<?php

$highlighted = highlight_string("<?php echo 1;",true); echo strpos($highlighted,"<span") !== false ? "Highlighted" : "Plain";

Output:

Highlighted

Example 2: Different Input or Behavior

<?php

echo is_string(highlight_string("<?php echo 2;",true)) ? "HTML returned" : "Failed";

Output:

HTML returned

Practical Example: Applying the Function

<?php

$sourceCode = "<?php echo 42;"; $highlighted = highlight_string($sourceCode,true); echo strlen($highlighted) . " bytes of HTML";

Output:

208 bytes of HTML

Important Behavior and Edge Cases

Never run or evaluate untrusted code; highlighting generates HTML that must be handled as markup intentionally.

Comparison With Related Functions

Common Beginner Mistakes

Key Takeaways

• Produces HTML-formatted syntax highlighting for PHP source code.
• Never run or evaluate untrusted code; highlighting generates HTML that must be handled as markup intentionally.
• highlight_file() highlights a file; highlight_string() highlights an in-memory source string.

Use highlight_string() for the specific operation demonstrated above. Check its prerequisites and handle failure conditions before using it with production data.