What It Means & How to Fix It in UE5 C++

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🧠 Why You’re Seeing This Error

LNK2028 is a linker error that means the linker found a reference to a token (function, variable, or method) — but it can’t resolve it, often due to mismatches between managed and native code, or missing implementations in C++ modules.

While it’s more common in /CLR (Common Language Runtime) projects, it can also appear in UE5 projects when:

• You’re integrating managed code (.NET) or using mixed-mode C++/CLI
• You call a function that’s declared but not defined
• You accidentally mix compiler settings (e.g., /clr vs /MT or /MD)
• You call external functions from DLLs that weren’t linked properly

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💥 Example Error Message

txtCopyEditLNK2028: unresolved token (0A000023) "public: void __clrcall MyFunction(void)" referenced in function ...

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🛠️ Example Scenario (In UE5)

You’re integrating a C++/CLI module or third-party .NET SDK into your Unreal Engine plugin:

// Declared somewhere in a mixed-mode header
public ref class DotNetHelper {
public:
    void DoSomething(); // ❌ Not defined or implemented in managed DLL
};

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✅ How to Fix LNK2028 in UE5 – Step-by-Step

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✔️ 1. Ensure All Declared Functions Are Fully Defined

Like LNK2019, this can occur when a function is declared but never implemented.

Fix:

void DotNetHelper::DoSomething() {
    // Implementation
}

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✔️ 2. Verify Any Managed Code Is Linked Properly

If you’re calling into .NET assemblies, make sure:

• You’ve included the correct .dll
• The symbols you’re calling are public and not inlined away
• You’ve enabled /clr in your plugin module if required

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✔️ 3. Avoid Mixing /clr and UE5 Runtime Unless Absolutely Necessary

UE5 isn’t designed for managed runtime integration. If you must integrate .NET or C++/CLI:

• Keep it isolated in a separate module
• Use DLL imports or COM interop instead of direct linking

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✔️ 4. Use DllImport or LoadLibrary() for .NET↔Native Interop

If calling into managed code from native UE5 C++, prefer runtime linking:

HMODULE MyDll = LoadLibrary(L"MyDotNetWrapper.dll");

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✅ Summary: How to Fix LNK2028 in UE5

Cause	Fix Example
Function declared but not implemented	Define the function in the correct module
.NET/CLR integration without linking	Add .NET DLL references properly
Mixed-mode C++/CLI integration error	Isolate or remove /clr usage from UE5 runtime code
Using P/Invoke or COM improperly	Use DllImport or LoadLibrary and check for symbol names