C2447: Missing Function Header (Old-Style Formal List?) in Unreal Engine 5 (UE5 C++) – What It Means & How to Fix It

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🧠 Why You’re Seeing This Error

The C2447 error means the compiler found a curly brace { (starting a function body), but it didn’t see a proper function declaration before it. It might look like you’re writing a function, but you’re missing the return type, parentheses, or even the function name.

The message “old-style formal list?” refers to a really outdated C syntax, and it’s Microsoft’s way of saying:

“This doesn’t look like a valid C++ function declaration.”

In Unreal Engine 5, this often happens when:

• You forget void or int32 before a function name
• You add {} directly after a variable or macro
• GENERATED_BODY() or UFUNCTION() is broken, which confuses the function parser

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💥 Example Error Message

error C2447: '{' : missing function header (old-style formal list?)

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🛠️ Example Code

void AMyActor::BeginPlay()
{
    Super::BeginPlay();

    InitLocation  // ❌ C2447: missing function header
    {
        // Do something
    }
}

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✅ How to Fix C2447 UE5 – Step-by-Step

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✔️ 1. Add the Missing Function Header (return type + parentheses)

Wrong:

InitLocation
{
    // ...
}

Fix:

void InitLocation()
{
    // ...
}

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✔️ 2. Don’t Use Curly Braces With Variables or Macro Calls

This error can show up if you’re using {} right after something that’s not a function.

Wrong:

FVector Location
{
    0.f, 0.f, 0.f
}; // ❌ This looks like a function to the compiler

Fix:

FVector Location = FVector(0.f, 0.f, 0.f); // ✅ Correct constructor syntax

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✔️ 3. Check for Broken Macros or Missing Semicolons

If a macro like GENERATED_BODY() or a variable declaration is broken, it can mess up the parser for the next function.

Make sure:

• GENERATED_BODY() is present and correct
• Every member ends in a ;
• You don’t have stray {} blocks

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✅ Summary: How to Fix C2447 in UE5

Cause	Fix
Missing return type or ()	Add function return type and parentheses (void MyFunc())
Using {} after variable	Use = with constructor or proper initialization
Broken macro or UFUNCTION	Check GENERATED_BODY(), UFUNCTION(), etc.
Mistyped function body	Always use full header: ReturnType Name(Params)