How to resolve the issue of mutable not working in C++?

In C++, the mutable keyword is used to modify a class member variable, indicating that the variable can be modified in a constant member function. If the mutable keyword is found to be ineffective, you can consider the following aspects to resolve the issue:

1. Ensure that member functions are declared as constant member functions: the “mutable” keyword is only effective for constant member functions. If a member function is not declared as a constant member function, the member variable cannot be modified even if the “mutable” keyword is used.
2. Check the access permission of member variables: If the access permission of member variables is private or protected, only functions within the class can modify the variable, and even using the mutable keyword cannot modify it outside the class.
3. Checking the constness of an object: If a constant object is used to call a member function, then even if the function is declared as a constant member function, it cannot modify the object’s member variables, even with the use of the mutable keyword.
4. Check the way the function is called: If a member function is called through a pointer or reference, and the pointer or reference is of const type, then even if the function is declared as a constant member function, it cannot modify the object’s member variables, even if the mutable keyword is used.
5. Check the version and settings of the compiler: Some compilers may have bugs in their support for the mutable keyword, so consider upgrading the compiler or checking its settings.

If none of the above methods work, it’s possible that there are other issues in the code causing the mutable keyword to malfunction, and further examination of the code logic is needed.