---
title: C26434
description: "Microsoft C++ Code Analysis warning C26434 for the C++ Core Guidelines case C.128."
ms.date: 08/21/2020
ms.topic: "conceptual"
f1_keywords: ["C26434"]
helpviewer_keywords: ["C26434"]
ms.assetid: 7f66477f-da66-444a-a6e3-44513d7d7e31
---
# C26434 DONT_HIDE_METHODS

> `Function 'derived::function' hides a non-virtual function 'base::function' (c.128).`

## C++ Core Guidelines

[C.128: Virtual functions should specify exactly one of virtual, override, or final](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md)

## Remarks

When you introduce a function that has the same name as a non-virtual function in a base class, you may get unexpected behavior. It's like introducing a variable name which conflicts with a name from an outer scope. For example, you may have intended to override a base class function. If the signatures of the functions don't match, the override you intended may turn into an overload instead. In general, name hiding is dangerous and error-prone.

In the Core Guidelines checks:

- Only non-overriding functions in the current class are checked.
- Only non-virtual functions of base classes are considered.
- No signature matching is performed. Warnings are emitted if unqualified names match.

## Example

This example demonstrates how a derived class can hide non-virtual functions, and how virtual functions allow both overloads and overrides:

```cpp
// C26434.cpp
struct Base
{
    virtual ~Base() = default;
    virtual void is_virtual() noexcept {}
    void not_virtual() noexcept {}
};

struct Derived : Base
{
    void is_virtual() noexcept override {}      // Okay, override existing function
    virtual void is_virtual(int i) noexcept {}  // Add a virtual overload for function
    void not_virtual() noexcept {}              // C26434, hides a non-virtual function
    virtual void not_virtual(int i) noexcept {} // C26434, and parameters ignored
};

```