In inheritance, there are some rules defined by C++, one of which is that the virables or the functions in the base class will be hidden if there are virables and functions with the same name.

It seems perfect, but it’s a pitfall of C++. Consider the following example.

#include <cstdio>
#include <iostream>

class Person {
public:
    explicit Person()
    { }
    ~Person()
    { }
    void
    sleep() const
    { printf("Person sleep\n"); }
    void
    sleep(const int sec) const
    { printf("Person sleep %d s\n", sec); }
private:
    Person(const Person&);
    const Person&
    operator=(const Person&);
};

class Student:public Person {
public:
    explicit Student()
    { }
    ~Person()
    { }
    void
    sleep() const
    { printf("Student sleep\n"); }
private:
    Student(const Student&);
    const Student&
    operator=(const Student&);
};

int
main(int argc, char **argv)
{
    Student stu;

    stu.sleep();
    stu.sleep(1);
    
    return 0;
}

This program won’t be compiled. It shows the following error:

test.cpp:39:16: error: no matching function for call to ‘Student::sleep(int)’
     stu.sleep(1);
                ^
test.cpp:39:16: note: candidate is:
test.cpp:25:5: note: void Student::sleep() const
     sleep() const
     ^
test.cpp:25:5: note:   candidate expects 0 arguments, 1 provided

That is because C++ will hide all the names in the base class as long as there are the same names in the derived class. In the Person class, sleep() and sleep(const int sec) have the same name. In the Student class, it only want to override the sleep() function, but the overriding cause the hiding of the sleep(const int sec) function!

So how to solve this problem? There are two methods so far.

  1. Don’t hide the names in the base class will using overloading functions.

  2. Use using directive to make the certain methods visible.

     class Student:public Person {
 public:
     using Person::sleep;
		
     explicit Student()
     { }
     ~Person()
     { }
     void
     sleep() const
     { printf("Student sleep\n"); }

Finally, another important thing should be stated. In the above example, I implement sleep() function in the definition of the class. Why do that? I have worked in some very large C++ projects and there are many implementation in the definition. In fact, this is so-called implicit inline. The compiler will inline the functions that are implemented in the class definition automatically. Therefore, it’s good to implement some small functions in the definition of class. And let the large function implement in another file. This will make my code more effecient and I will follow this guide in the future.