Thread: constructor syntax

Hello, I have the following constructor,

Code:

class COperator
{
  public:COperator::COperator( HINSTANCE hInst ) : 
                                                  m_hDlg( NULL ),
                                                  m_pTapi( NULL ),
                                                  m_pCall( NULL )
                                                 {};
};

What I don't understand is the need for the '::' after the COperator. What is the difference when compared to:

Code:

class COperator
{
  public:
    COperator( HINSTANCE hInst ) : 
                       m_hDlg( NULL ),
                       m_pTapi( NULL ),
                       m_pCall( NULL )
                       {};
};

If there are any advantages when it comes to using ::, it would be helpful to know.

Thanks.

>If there are any advantages when it comes to using ::, it would be helpful to know.
There's no need for scope resolution when you're defining a member function within the scope of the class declaration. It's only needed when you separate the declaration and definition:

Code:

class COperator {
public:
  COperator(HINSTANCE hInst);
};

COperator::COperator( HINSTANCE hInst )
  : m_hDlg( NULL )
  , m_pTapi( NULL )
  , m_pCall( NULL )
{}

Ok thankyou. The code the was taken from a Microsoft sample, and I had never used the operator in that way. I have only used it when I sperate the code from class definition, i.e. using a class1.h and class1.cpp for example.

objetc o(10);
is equivalent
with
object o = 10;

Only if the constructor isn't declared as explicit:

Code:

#include <iostream>

using namespace std;

class test1 {
  int i;
public:
  test1(int init)
    : i(init)
  {}
};

class test2 {
  int i;
public:
  explicit test2(int init)
    : i(init)
  {}
};

int
main()
{
  test1 a(10);  // Okay
  test2 b(10);  // Okay
  test1 c = 10; // Okay
  test2 d = 10; // Error! Implicit construction unavailable
}

how can i use "=" in this case
object o(10, 20);

You can't. It only works for constructors that take a single argument. You could manage something similar though by passing an array:

Code:

#include <iostream>

using namespace std;

class test1 {
  int i, j;
public:
  test1(int init[])
    : i(init[0])
    , j(init[1])
  {}
};
int
main()
{
  int   args[] = {10, 20};
  test1 a = args;
}