C++ Visual Studio

Understanding the C++ Compiler Error C2371 - Redefinition of WCHAR

If you are a C++ developer working with Visual Studio, you may have encountered the frustrating compiler error C2371: “Redefinition of WCHAR.” This error typically arises when including certain header files, particularly when your project settings are configured to use Multi-Byte Character Set (MBCS). Let’s dive into what this error means, why it occurs, and how you can effectively resolve it.

The Problem: What Does Error C2371 Mean?

When you see the error message related to WCHAR, it denotes a conflict in the definition of this type due to multiple inclusions of header files:

error C2371: 'WCHAR': redefinition; different basic types

The error typically arises from including the odbcss.h header file, which in turn includes other Windows headers like winnt.h. It can be particularly problematic if the WCHAR type is re-declared with different basic types.

Why Does This Happen?

This issue is a common pitfall when:

  • Your project is set up to compile with MBCS character settings, and
  • The included headers have conflicting definitions of the same type, in this case, WCHAR.

This has been acknowledged as a known issue, and many developers have experienced similar conflicts.

The Solution: Changing Your Project Settings

To resolve the C2371 error effectively, you have a couple of options to consider:

1. Change to Unicode Compilation

One of the simplest ways to avoid the C2371 error is to change your project settings to use Unicode instead of MBCS. This can typically be done from the project properties in Visual Studio:

  • Step 1: Open your project in Visual Studio.
  • Step 2: Right-click on your project in the Solution Explorer and select Properties.
  • Step 3: Navigate to the Configuration Properties -> General section.
  • Step 4: Look for the Character Set option and change it from Use Multi-Byte Character Set to Use Unicode Character Set.
  • Step 5: Rebuild your project.

2. Review Header File Inclusions

Sometimes, the root cause may also lie in how header files are included in your project:

  • Check for redundancy in your includes: Make sure you are not inadvertently including headers multiple times.
  • Isolate includes specific to MBCS and Unicode situations, so they do not overlap.

3. Consulting Resources

If you’re still experiencing issues, consider checking Microsoft’s feedback on this known bug. More information can be found on the Microsoft Connect site.

Final Thoughts

Encountering the C++ Compiler error C2371 can be a roadblock in your development process, but with a little understanding of the problem and the right adjustments to your project settings, you can move past this hurdle. Transitioning to Unicode is often the most straightforward solution, but always consider reviewing your project’s structure and included headers to prevent similar issues in the future.

By being vigilant about these types of conflicts, you can enhance your coding experience and keep your development process smooth. Happy coding!