MISRA C++:2023 Rule 13.3.1

User-declared member functions shall use the virtual, override and final specifiers appropriately

Since R2024b

Description

Rule Definition

User-declared member functions shall use the virtual, override and final specifiers appropriately. ¹

Rationale

To make the design of a class easy to understand, this rule specifies the appropriate use of the virtual, override, and final specifiers for user-declared member functions and destructors:

• Use the specifier virtual if the member function is a new virtual function that does not override a function from a base class.

• Use the specifier override if the member function is a virtual function that overrides a virtual function from a base class and permits further overrides in subsequent derived classes.

• Use the specifier final if the member function is a virtual function that overrides a function from a base class and does not permit further overrides in subsequent derived classes.

Other combinations of these specifiers are permissible in the C++ standard but violate this rule because they can make the code harder to understand.

Polyspace Implementation

Polyspace^® reports a violation if any of these conditions are true:

• A virtual function in a derived class uses the specifier virtual in addition to override or final.

• A virtual function in a base class uses the specifier override or final in addition to virtual.

Troubleshooting

If you expect a rule violation but Polyspace does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Inappropriate Combination of Specifiers for User-Defined Member Function

In this example, the derived class Dog uses the specifier virtual in the definition of DOg::makeSound() in addition to the specifier override. This use of the of the virtual and override specifiers is permitted in the C++ standard but makes the code difficult to understand. Polyspace reports a violation.

#include <iostream>

// Base class
class Animal {
public:
    // Virtual function
    virtual void makeSound() const{
        std::cout << "Some generic animal sound" << std::endl;
    }

    // Virtual destructor
    virtual ~Animal() = default;
};

// Derived class 1
class Dog : public Animal {
public:
    // Override the virtual function
    virtual void makeSound() const override {  // Noncompliant
        std::cout << "Bark" << std::endl;
    }
};

// Derived class 2
class Cat : public Animal {
public:
    // Override the virtual function
    void makeSound() const override { //Compliant
        std::cout << "Meow" << std::endl;
    }
};

The derived virtual function Cat::makeSound() is compliant because it uses the specifier override.

Check Information

Group: Derived classes

Category: Required

Version History

Introduced in R2024b