📎 Classic ASP – #include – Reuse Code Across Pages with Server-Side Includes

🧲 Introduction – What Is #include in Classic ASP?

In Classic ASP, the #include directive is used to reuse code across multiple .asp pages. This is known as a Server-Side Include (SSI) and it allows you to place shared functions, HTML headers, footers, or configuration in a single file and include it wherever needed.

🎯 In this guide, you’ll learn:

• How to use #include for code reusability
• Difference between virtual and file includes
• Best practices for layout, functions, and error prevention
• Examples of common uses like headers, footers, and constants

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📌 Syntax of #include

<!-- #include virtual="path" -->
<!-- #include file="relative_path" -->

These lines must be placed outside of <% %> script blocks.

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🔀 #include file vs #include virtual

Directive	Path Type	Example
#include file	Relative path	<!--#include file="includes/footer.asp"-->
#include virtual	Absolute path (from site root)	<!--#include virtual="/includes/header.asp"-->

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✅ Example – Including a Header and Footer

📄 /includes/header.asp

<h1>My Website Header</h1>
<hr>

📄 /includes/footer.asp

<hr>
<p>© 2025 My Website</p>

📄 /index.asp

<!--#include virtual="/includes/header.asp"-->

<p>Welcome to the homepage!</p>

<!--#include virtual="/includes/footer.asp"-->

🧪 Output:

<h1>My Website Header</h1>
-------------------------
Welcome to the homepage!
-------------------------
© 2025 My Website

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🧱 Reusing Functions with #include

📄 mathlib.asp

<%
Function Add(x, y)
    Add = x + y
End Function
%>

📄 main.asp

<!--#include file="mathlib.asp"-->
<%
Dim result
result = Add(5, 3)
Response.Write "Sum: " & result
%>

🧪 Output: Sum: 8

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⚠️ Rules and Limitations

Rule	Explanation
Must be outside <% %> tags	ASP will error otherwise
No dynamic includes (#include can’t use variables)	All paths must be static
No conditional includes	Includes are parsed before execution

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💡 Common Uses of #include

• ✅ Site-wide headers and footers
• ✅ Shared constants or config settings
• ✅ Database connection file
• ✅ Utility functions or error handlers

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📘 Best Practices for Classic ASP #include

✅ Do:

• Use virtual for root-relative includes across folders
• Use file for including files within the same directory
• Keep reusable logic (functions, constants) in .asp include files

❌ Avoid:

• Deep nested includes
• Including large blocks of unrelated logic
• Placing #include inside script tags

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📌 Summary – Recap & Next Steps

The #include directive in Classic ASP is a powerful feature that promotes modular, maintainable code. Whether you’re building a layout or reusing functions, #include keeps your project DRY (Don’t Repeat Yourself).

🔍 Key Takeaways:

• Use #include file and #include virtual to reuse HTML or VBScript
• Includes must be static and outside ASP blocks
• Perfect for headers, footers, config, and utility code

⚙️ Real-world Use Cases:

• Add site-wide navigation and branding
• Centralize database connection logic
• Maintain consistency across 100s of .asp pages

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❓ FAQs – Classic ASP #include

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❓ Can I use a variable in an #include path?
❌ No. #include paths must be static strings—they are evaluated before ASP code runs.

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❓ What’s the difference between file and virtual?
✅ file uses a relative path, while virtual starts from the site root (IIS virtual directory).

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❓ Can I place #include inside <% %>?
❌ No. Includes must be declared outside ASP script blocks.

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