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C++ constructor_01

Date: 2020-02-25Last modified: 2024-11-02
C++constructor

Table of contents

class A {
public:
  A()
  {
  }
  int i; // not initialized
  int j = 5;
};

class B {
public:
  B() = default;
  int i; // will be initialized with 0
  int j; // will be initialized with 0
};

int main( [[maybe_unused]] int argc, [[maybe_unused]] char **argv )
{
  for( int i = 0; i < 5; ++i ) {
    A *pa = new A();
    B *pb = new B();
    cout << "A.i = " << pa->i << " A.j = " << pa->j << " without default constructor" << endl;
    cout << "B.i = " << pb->i << " B.j = " << pb->j << " with default constructor" << endl;
    delete pa;
    delete pb;
  }
  return 0;
}

Possible output

A.i = 0 A.j = 5 without default constructor
B.i = 0 B.j = 0 with default constructor
A.i = -161976930 A.j = 5 without default constructor
B.i = 0 B.j = 0 with default constructor
A.i = -161976834 A.j = 5 without default constructor
B.i = 0 B.j = 0 with default constructor
A.i = -161976930 A.j = 5 without default constructor
B.i = 0 B.j = 0 with default constructor
A.i = -161976834 A.j = 5 without default constructor
B.i = 0 B.j = 0 with default constructor

References