What It Means & How to Fix It in UE5 C++
🧠 Why You’re Seeing This Error
LNK1120 is a summary linker error — it tells you that one or more symbols (functions, variables, etc.) were declared but never defined, and the linker couldn’t resolve them.
In UE5, this error always shows up after other errors like LNK2019 or LNK2001 and usually appears at the bottom of the build log.
💥 Example Error Message
fatal error LNK1120: 1 unresolved externals
🛠️ Example Scenario
You might see this after something like:
error LNK2019: unresolved external symbol "void AMyActor::DoSomething()" ...
fatal error LNK1120: 1 unresolved externals
This means the root problem is with DoSomething(), and LNK1120 is just saying:
“We couldn’t finish linking because we’re still missing 1 symbol.”
✅ How to Fix LNK1120 in UE5 – Step-by-Step
✔️ 1. Scroll Up to Find the Real Error
LNK1120 doesn’t tell you which symbol is missing — it’s just the summary. The real cause will be shown above it, usually as a LNK2001 or LNK2019.
✔️ 2. Fix the Missing Symbol(s)
Common fixes:
- Add the missing function definition in your
.cppfile - Define global/static variables in one place
- Correct a function signature mismatch
- Add missing
.Build.csmodule dependencies
✔️ 3. Rebuild the Project After Fixing the Symbol
Once the original error is fixed, LNK1120 will disappear automatically — it never occurs on its own.
✅ Summary: How to Fix LNK1120 in UE5
| Cause | Fix Example |
|---|---|
| Function declared but not defined | Add the definition in the .cpp |
| Global/static variable undeclared | Add int32 MyVar = 0; in one .cpp |
| Missing module reference | Add module to .Build.cs |
| Signature mismatch | Ensure header and source declarations match exactly |
