Why does abstract base class need explicit default constructor?-CodePudding

For below code,

#include <iostream>

class virtualBase {
public:
  virtual void printName() = 0;

//   virtualBase() = default;

private:
  virtualBase(const virtualBase &) = delete; // Disable Copy Constructor
  virtualBase &
  operator=(const virtualBase &) = delete; // Disable Assignment Operator
};

class derivedClass : public virtualBase {
public:
  void printName() { std::cout << "Derived name" << std::endl; };
  derivedClass() {};
  ~derivedClass() = default;
};

int main() {
  derivedClass d;
  d.printName();
  return 0;
}

I need to uncomment the default constructor definition in base class for the compilation to succeed.

I am seeing the following compilation error:

test.cpp: In constructor ‘derivedClass::derivedClass()’:
test.cpp:18:18: error: no matching function for call to ‘virtualBase::virtualBase()’
   18 |   derivedClass() {};
      |                  ^
test.cpp:10:3: note: candidate: ‘virtualBase::virtualBase(const virtualBase&)’ <deleted>
   10 |   virtualBase(const virtualBase &) = delete; // Disable Copy Constructor
      |   ^~~~~~~~~~~
test.cpp:10:3: note:   candidate expects 1 argument, 0 provided

My understanding is that compiler provides it own default constructor esp in case like this where the class is really simple.

What am I missing here?

Thanks

CodePudding user response：

Declaring any constructor explicitly prevents declaration of the implicit default constructor.

You do declare the copy constructor explicitly (even if you then define it as deleted).