What It Means & How to Fix It

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🧠 Why You’re Seeing This Error

The C2061 error means the compiler found a type, class name, or identifier it doesn’t recognize, usually in a function parameter, return type, or member declaration.

In UE5, this typically happens when:

• You forgot to include the header for a type (especially UObject-derived classes or structs)
• You declared a function with a class/struct that hasn’t been declared yet
• You misused a macro or typo’d a type name
• A forward declaration isn’t enough (e.g. using a type by value instead of by pointer)

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💥 Example Error Message

error C2061: syntax error: identifier 'FMyStruct'

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🛠️ Example Code

// MyActor.h

UCLASS()
class AMyActor : public AActor
{
    GENERATED_BODY()

    FMyStruct Data; // ❌ C2061: Compiler doesn’t know what FMyStruct is
};

If FMyStruct is declared in another header — and you didn’t include that header here — the compiler doesn’t recognize the type.

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✅ How to Fix C2061 in UE5 – Step-by-Step

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✔️ 1. Include the Header That Declares the Type

Fix:

#include "MyStruct.h" // ✅ Now FMyStruct is known

If FMyStruct is defined in MyStruct.h, you must include it before using it by value.

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✔️ 2. Use a Forward Declaration Only If You Use a Pointer or Reference

If you want to avoid including the full header, you can forward-declare the class/struct — but only if you’re not using it by value.

Works:

class UMyComponent;

UPROPERTY()
UMyComponent* Component; // ✅ Pointer is okay with forward-declare

Does NOT work:

UMyComponent Component; // ❌ Needs full definition

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✔️ 3. Check for Typos in Type Names

UE5 types often start with prefixes: A, U, F, or E.

Wrong:

FStirng Name; // ❌ Typo

Fix:

FString Name; // ✅

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✔️ 4. Make Sure Macros Like USTRUCT and GENERATED_BODY Are Intact

Missing or malformed Unreal macros can cause C2061 even when the type exists.

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✅ Summary: How to Fix C2061 in UE5

Cause	Fix Example
Type used without including header	#include "MyStruct.h"
Using undeclared class by value	Include full definition or use a pointer
Forward declaration misused	Only use forward-declare with pointers or refs
Typos in Unreal type names	Watch out for spelling (e.g., FString, not FStirng)