Coding⏱️ 3 min read📅 2026-06-11

How to Fix: sudo pecl install intl and get fatal error: 'ext/standard/php_smart_str.h' file not found

Error installing PHP intl extension due to missing file. Solution involves specifying ICU library locations.

Quick Answer: Specify the location of ICU libraries and headers by answering the prompt correctly.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. ✅ Best Solutions to Fix It
  3. 💡 Conclusion

The error 'ext/standard/php_smart_str.h' file not found when installing intl using pecl is a common issue that affects users of PHP and its extensions. This error occurs because the php_smart_str.h header file, which is required for the intl extension, is missing from your system. As a result, the installation process fails, leaving you with a broken intl extension.

This situation can be frustrating, especially when trying to install a critical extension like intl for Moodle. However, by following the steps outlined in this guide, you should be able to resolve the issue and successfully install the intl extension.

🔍 Why This Happens

  • The primary reason for this error is that the php_smart_str.h header file is not installed on your system. This file is part of the standard PHP distribution, but it may not be included by default in some systems or configurations.
  • An alternative reason could be that the php_smart_str.h file is corrupted or missing due to a previous installation issue or system update.

✅ Best Solutions to Fix It

Specify ICU libraries and headers manually

  1. Step 1: To resolve this issue, you need to specify the location of the ICU (International Components for Unicode) libraries and headers. This will tell pecl where to find the required php_smart_str.h file. To do this, run the following command: Specify where ICU libraries and headers can be found [DEFAULT] :
  2. Step 2: You should enter the path to the ICU library directory, which is usually located at /usr/include/icu4c or /usr/local/include/icu4c. For example: /usr/include/icu4c. Press Enter to continue.
  3. Step 3: After specifying the correct location, pecl will attempt to install the intl extension again. If you encounter any further issues, you may need to reinstall the ICU library and headers.

Reinstall PHP and its extensions

  1. Step 1: Another approach is to reinstall PHP and its extensions from scratch. This will ensure that all required libraries and headers are installed correctly.
  2. Step 2: To do this, you can remove the existing PHP installation using apt-get or Homebrew (depending on your system), and then install a fresh copy of PHP using the recommended package manager.

💡 Conclusion

By following these steps, you should be able to resolve the 'ext/standard/php_smart_str.h' file not found error when installing intl using pecl. Remember to specify the correct location of the ICU libraries and headers or reinstall PHP and its extensions if necessary.

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