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What’s the Difference Between highlight_file and highlight_string? How to Choose the Right PHP Highlight Function

gitbox 2025-10-01

1. highlight_file Function

The highlight_file function is used to highlight the contents of a specified file. Its syntax is as follows:

<span><span><span class="hljs-title function_ invoke__">highlight_file</span></span><span>(</span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$filename</span></span><span>, </span><span><span class="hljs-keyword">bool</span></span><span> </span><span><span class="hljs-variable">$return</span></span><span> = </span><span><span class="hljs-literal">false</span></span><span>): </span><span><span class="hljs-keyword">string</span></span><span>|</span><span><span class="hljs-literal">false</span></span></span>

  • Parameters:

    • $filename: The path of the file to be highlighted.

    • $return: An optional boolean. If set to true, the function returns the highlighted code instead of outputting it directly. If set to false (default), it outputs the highlighted code directly.

  • Return Value:

    • If $return is true, the function returns the highlighted code as a string.

    • If $return is false (default), the highlighted code is output directly.

Example:

<span><span><span class="hljs-title function_ invoke__">highlight_file</span></span><span>(</span><span><span class="hljs-string">'example.php'</span></span><span>);
</span></span>

This code will directly output the highlighted contents of the example.php file.

2. highlight_string Function

The highlight_string function highlights a PHP code string. Its syntax is as follows:

<span><span><span class="hljs-title function_ invoke__">highlight_string</span></span><span>(</span><span><span class="hljs-keyword">string</span></span><span> </span><span><span class="hljs-variable">$str</span></span><span>, </span><span><span class="hljs-keyword">bool</span></span><span> </span><span><span class="hljs-variable">$return</span></span><span> = </span><span><span class="hljs-literal">false</span></span><span>): </span><span><span class="hljs-keyword">string</span></span><span>|</span><span><span class="hljs-literal">false</span></span></span>

  • Parameters:

    • $str: The PHP code string to highlight.

    • $return: An optional boolean. If set to true, the function returns the highlighted code instead of outputting it directly. If set to false (default), it outputs the highlighted code directly.

  • Return Value:

    • If $return is true, the function returns the highlighted code as a string.

    • If $return is false (default), the highlighted code is output directly.

Example:

<span><span><span class="hljs-variable">$code</span></span><span> = </span><span><span class="hljs-string">'&lt;?php echo "Hello, World!"; ?&gt;'</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">highlight_string</span></span><span>(</span><span><span class="hljs-variable">$code</span></span><span>);
</span></span>

This code will directly output the highlighted $code string.

3. Main Differences Between highlight_file and highlight_string

Although both functions highlight PHP code, the differences mainly lie in the input type and usage scenarios:

  1. Input Type:

    • highlight_file requires a file path, suitable for highlighting the contents of a file.

    • highlight_string works directly with a string, suitable for dynamically generated or existing code strings.

  2. Use Cases:

    • Use highlight_file when you need to highlight PHP code from a file.

    • Use highlight_string when you need to highlight dynamically generated PHP code snippets.

  3. Return Method:

    • Both functions allow you to choose between direct output or returning the highlighted string by setting the $return parameter.

4. How to Choose the Right Highlight Function

  1. If you have a file to highlight and do not want to load the file contents into memory as a string, highlight_file is the simpler choice.

  2. If you are dealing with a string, such as user-submitted PHP code or dynamically generated code snippets, highlight_string is more appropriate.

  3. If you need the highlighted content as a string instead of outputting it directly, set the $return parameter to true, then use echo or another method to display it.

5. Summary

  • highlight_file and highlight_string are both tools for highlighting PHP code, but highlight_file is suited for files, while highlight_string is better for strings.

  • The choice depends on the type of data you need to handle: file contents or code strings.

Understanding their differences and choosing appropriately can help you implement code highlighting more efficiently during development and improve the user experience.

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