C-Sharp C++ Com Interop

Understanding #import Errors with .NET Out-of-Proc Servers in C++

When integrating .NET components with C++ applications, developers often encounter challenges, particularly when using the #import directive to include type libraries (TLB). One common situation arises when you attempt to #import a .NET out-of-proc server but instead are met with a series of perplexing compilation errors. In this post, we’ll address this problem and provide a detailed solution to help you move forward seamlessly.

The Problem: Error Messages During #import

Imagine you’re working on a C++ program where you need to incorporate functionality from a .NET out-of-proc server. You confidently use the #import directive on the server’s TLB file but are instead met with error messages like:

z:\server.tlh(111) : error C2146: syntax error : missing ';' before identifier 'GetType'
z:\server.tlh(111) : error C2501: '_TypePtr' : missing storage-class or type specifiers
...

These types of errors can be frustrating and can halt your development progress. They often suggest problems with how the type library is being interpreted during the import process.

Common Errors Explained

Here are explanations for some of the errors you might encounter:

  • Syntax error : missing ‘;’: Indicates that the compiler couldn’t resolve an identifier, often due to a missing declaration.
  • Missing storage-class or type specifiers: Suggests that a type expected by the compiler is not being defined correctly during the import.
  • Unexpected end of file found: This usually implies that the compiler reached the end of the file without properly interpreting all required definitions, signifying a parsing issue.

The Solution: Modifying the #import Directive

Fortunately, the solution is straightforward once you understand how to optimize your #import usage. By adopting a couple of strategies, you can avoid these pitfalls effectively.

1. Use no_namespace and raw_interfaces_only Options

Adjust your #import directive to include the no_namespace and raw_interfaces_only options. Here’s how you would modify your import statement:

#import "server.tlb" no_namespace named_guids

Why These Options Matter:

  • no_namespace: This prevents the compiler from wrapping the imported definitions in a namespace, which can lead to cleaner code and fewer conflicts.
  • named_guids: This allows for COM interfaces to use their GUIDs in a more manageable way, promoting easier access to the component’s methods.

2. Prefer TLBEXP.EXE Over REGASM.EXE

Using TLBEXP.EXE (Type Library Exporter) instead of REGASM.EXE to generate the type library can also help resolve these issues. TLBEXP.EXE is specifically designed for creating type libraries, whereas REGASM.EXE can introduce complications depending on how your assembly registers itself.

Conclusion

By following the two key adjustments in your #import directive and using the recommended exporting tool, you can alleviate the common issues faced while trying to integrate .NET out-of-proc servers in your C++ applications. Addressing these concerns not only streamlines your programming experience but also enhances the interoperability between C++ and .NET components.

Implement these strategies today and watch your development process become significantly smoother!