What It Means & How to Fix It

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🧠 Why You’re Seeing This Error

C2872 means that multiple declarations of a symbol exist, and the compiler doesn’t know which one you meant. It’s a namespace collision issue — and in UE5, this usually means two different APIs define the same name (like uint8, Text, Vector, etc.).

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💥 Example Error Message

error C2872: 'Vector': ambiguous symbol

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🛠️ Example Code

using namespace UnrealNamespace;
using namespace MathLibrary;

Vector Position; // ❌ C2872: Which Vector do you mean?

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✅ How to Fix C2872 in UE5 – Step-by-Step

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✔️ 1. Use Fully Qualified Names

Be explicit about which version of the symbol you want.

Fix:

FVector Position;         // ✅ Unreal's FVector
MathLibrary::Vector V2;   // ✅ Another library’s Vector

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✔️ 2. Avoid Using using namespace in Headers

Putting using namespace in a .h file pollutes global scope and increases the risk of conflicts — especially in UE5 projects that use many modules.

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✔️ 3. Use typedefs or using to Rename If Needed

namespace ThirdParty {
    class Vector { ... };
}

using TPVector = ThirdParty::Vector;
TPVector V; // ✅ Avoids namespace collision

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✅ Summary: How to Fix C2872 in UE5

Cause	Fix Example
Multiple types with same name	Use FVector, ThirdParty::Vector, etc.
using namespace conflict	Avoid globally; use fully qualified names
Typedef to rename	Use using MyVector = Namespace::Vector;