Unraveling the Mystery: Can You Link Implicitly against an Import Lib and Call a Function Exported by Ordinal?

Introduction

As a seasoned developer, you’ve likely encountered the conundrum of linking implicitly against an import library and calling a function exported by ordinal. But is it possible? The answer might surprise you. In this article, we’ll delve into the world of import libraries, ordinal exports, and implicit linking, providing clear instructions and explanations to help you overcome this challenge.

What are Import Libraries and Ordinal Exports?

Before we dive into the meat of the matter, let’s define the key terms:

• Import Library: An import library is a static library that contains the stubs for the functions exported by a DLL. It’s generated by the linker when creating a DLL and is used to resolve imports at link-time.
• Ordinal Export: An ordinal export is a function exported by a DLL using an ordinal number instead of a name. This means that instead of exporting a function with a specific name, the DLL exports it with a numerical identifier.

The Problem: Implicit Linking and Ordinal Exports

So, what’s the issue? When you link implicitly against an import library, the linker resolves the imports by matching the function names. However, when a function is exported by ordinal, the linker doesn’t know how to resolve the import. This is because ordinal exports don’t have a name to match.

This poses a challenge when trying to call a function exported by ordinal from an import library. But fear not, dear developer, for there is a solution!

Solution 1: Using GetProcAddress

One way to call a function exported by ordinal is to use the GetProcAddress function. This allows you to retrieve the address of the exported function and call it directly. Here’s an example:

// Assume the DLL exports a function with ordinal 123
HMODULE hModule = LoadLibrary("mydll.dll");
if (hModule == NULL) {
  // Handle load failure
}

// Get the address of the exported function
FARPROC pFunc = GetProcAddress(hModule, MAKEINTRESOURCE(123));
if (pFunc == NULL) {
  // Handle function not found
}

// Call the function
typedef int (__stdcall *MyFuncType)();
MyFuncType pMyFunc = (MyFuncType)pFunc;
int result = pMyFunc();

This approach works, but it requires manual management of the DLL loading and function retrieval. Let’s explore an alternative solution.

Solution 2: Using a Proxy Function

A more elegant solution is to create a proxy function in your import library that calls the ordinal-exported function. This way, you can link implicitly against the import library and call the proxy function, which will in turn call the ordinal-exported function.

Here’s an example:

// mylib.lib (import library)
extern "C" {
  __declspec(dllexport) int __stdcall MyProxyFunc() {
    HMODULE hModule = GetModuleHandle("mydll.dll");
    if (hModule == NULL) {
      // Handle module not found
    }

    FARPROC pFunc = GetProcAddress(hModule, MAKEINTRESOURCE(123));
    if (pFunc == NULL) {
      // Handle function not found
    }

    typedef int (__stdcall *MyFuncType)();
    MyFuncType pMyFunc = (MyFuncType)pFunc;
    return pMyFunc();
  }
}

In this example, the import library exports a proxy function MyProxyFunc, which calls the ordinal-exported function using GetProcAddress. Your application can then link implicitly against the import library and call the proxy function.

Conclusion

In conclusion, linking implicitly against an import library and calling a function exported by ordinal is possible, but it requires some creative problem-solving. By using GetProcAddress or creating a proxy function in your import library, you can overcome this challenge and successfully call the ordinal-exported function.

Best Practices and Considerations

When working with import libraries and ordinal exports, keep the following best practices and considerations in mind:

• Use named exports whenever possible: Named exports are easier to manage and link against than ordinal exports.
• Document your ordinal exports: Clearly document the ordinal exports and their corresponding functions to avoid confusion.
• Use a consistent naming convention: Use a consistent naming convention for your proxy functions to avoid naming conflicts.
• Test your code thoroughly: Test your code extensively to ensure that the proxy function or GetProcAddress approach works correctly.

Frequently Asked Questions

Here are some frequently asked questions related to linking implicitly against an import library and calling a function exported by ordinal:

Q: Can I use ordinal exports with C++ classes?	A: No, ordinal exports are not compatible with C++ classes. Use named exports instead.
Q: How do I handle versioning with ordinal exports?	A: Use a version-aware approach when exporting functions with ordinals, such as using a version-specific ordinal range.
Q: Can I use ordinal exports with dynamic linking?	A: No, ordinal exports are typically used with static linking. Use named exports for dynamic linking.

Conclusion

In this article, we’ve explored the challenges of linking implicitly against an import library and calling a function exported by ordinal. By using creative solutions like GetProcAddress or creating a proxy function, you can overcome these challenges and successfully call the ordinal-exported function. Remember to follow best practices and considerations to ensure your code is robust and maintainable.

So, the next time you’re faced with this conundrum, you’ll know exactly what to do. Happy coding!

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