C2275: Illegal Use of This Type as an Expression in Unreal Engine 5 (UE5 C++) – What It Means & How to Fix It

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Why You’re Seeing This Error

The C2275 error means the compiler thinks you’re trying to use a type name as if it were a variable or expression — which usually means:

• You used a type name in the wrong place (like calling FVector without declaring a variable)
• You forgot a type like int32 when declaring a variable
• You’re using a custom struct or class without including its header
• The syntax is invalid — maybe you’re missing parentheses, commas, or semicolons

In Unreal Engine 5, this often happens when using Unreal types (FVector, FString, etc.) without proper context, or when defining variables without a type keyword.

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Example Error Message

error C2275: 'FVector': illegal use of this type as an expression

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Example Code

void AMyActor::BeginPlay()
{
    FVector; //  C2275: illegal use of this type as an expression
}

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How to Fix C2275 UE5 – Step-by-Step

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1. Make Sure You’re Declaring a Variable, Not Just Typing a Type

Unreal types like FVector, FString, int32, etc. need a variable name and often an initializer.

Fix:

FVector Location = GetActorLocation(); //  Correct use of FVector

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2. Avoid Using Types as Standalone Statements

This won’t work:

FVector; //  Invalid — not a complete statement

This will:

FVector MyLocation; //  Declaring a variable

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3. Include Headers for Custom Types or UE Types

If you’re using a custom struct or a UE5 class (like FMyData or FMyStruct) without including the correct header, the compiler gets confused.

Fix:

#include "MyStruct.h" //  Always include your custom types

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4. Make Sure You Didn’t Forget a Type in a Declaration

Wrong:

Location = GetActorLocation(); //  What is Location? The compiler doesn't know

Fix:

FVector Location = GetActorLocation(); //  Now the type is clear

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Summary: How to Fix C2275 in UE5

Cause	Fix
Using a type without a variable	Add a variable name and initializer
Forgetting the type in a declaration	Specify the type explicitly (FVector, int32, etc.)
Missing include for a custom type	Include the correct header file
Typing a type alone	Don’t write just FVector;, use FVector VarName;