Constructors with default parameters in Header files

Question

I have a cpp file like this:

#include Foo.h;
Foo::Foo(int a, int b=0)
{
    this->x = a;
    this->y = b;
}

How do I refer to this in

Answer 1

.h:

class Foo {
    int x, y;
    Foo(int a, int b=0);
};

.cc:

#include "foo.h"

Foo::Foo(int a,int b)
    : x(a), y(b) { }

You only add defaults to declaration, not implementation.

Answer 2

The default parameter needs to be written in header file.

Foo(int a, int b = 0);

In the cpp, while defining the method you can not specify the default parameter. However, I keep the default value in the commented code so as it is easy to remember.

Foo::Foo(int a, int b /* = 0 */)

Answer 3

The header file should have the default parameters, the cpp should not.

test.h:

class Test
{
public:
    Test(int a, int b = 0);
    int m_a, m_b;
}

test.cpp:

Test::Test(int a, int b)
  : m_a(a), m_b(b)
{

}

main.cpp:

#include "test.h"

int main(int argc, char**argv)
{
  Test t1(3, 0);
  Test t2(3);
  //....t1 and t2 are the same....

  return 0;
}

Answer 4

You need to put the default arguments in the header, not in the .cpp file.