Why You’re Seeing This Error

You’re getting this error because the compiler can’t find the definition of the identifier you’re trying to use. In Unreal Engine projects, this often happens when:

• You misspell a variable, function, or class name.
• You forgot to include a header file that declares the identifier.
• You’re referencing a class like AMyActor but you just typed MyActor without the Unreal naming prefix (A for Actors, U for UObject-derived classes, etc.).
• You’re accessing something outside its scope, like a variable declared in another function or a class that hasn’t been included properly.

---

💥 Example Error Message

error C2065: 'MyActor' : undeclared identifier

---

🛠️ Example Code With Comments

void AMyGameMode::Spawn() {
    MyActor* Actor = GetWorld()->SpawnActor<MyActor>();
    // C2065 ERROR: 'MyActor' is not declared in this scope.
    // The compiler doesn't know what 'MyActor' refers to.
    // Likely causes:
    // - Forgot to include the MyActor.h header.
    // - 'MyActor' should actually be 'AMyActor' (Unreal Actor class naming).
}

---

✅ How to Fix It

✔️ 1. Check for Typos

Make sure you’re using the correct Unreal class naming conventions:

• A prefix for Actor classes (e.g., AMyActor)
• U for UObject-based classes (e.g., UMyComponent)
• F for structs (FVector, FString)
• E for enums

✔️ 2. Include the Correct Header

#include "MyActor.h"
// This makes the definition of AMyActor visible in this file.

✔️ 3. Use the Right Class Name

If your class is defined as AMyActor, update your code like this:

void AMyGameMode::Spawn() {
    AMyActor* Actor = GetWorld()->SpawnActor<AMyActor>();
    // Now this will compile, because AMyActor is a valid and declared class.
}

✔️ 4. Forward Declare (if possible)

If you’re only referencing the class via pointer or reference, and don’t need full type info (e.g., in a header file), you can forward-declare it:

class AMyActor;  // Tells the compiler that AMyActor exists.

---

🧩 Bonus Tip: IntelliSense Can Help

In Visual Studio, if you see red squiggly lines under a class name and no suggestions when you hover, that’s a strong sign the class isn’t declared or imported properly.