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.

Quote:

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reelated to the topic:
this
objetc o(10);
is equivalent
with
object o = 10;

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

---

Making an operator (in your case the '=' sign) work with classes requires you to write an overloaded operator. The same operator can be overloaded multiple times for the same class, as long as the value on the right are of diffrent types. an example of this is cout.... when you type...

Code:

---

int x=1;
cout<<x;

---

the '<<' operator is overloaded for int's, but '<<' is overloaded for many diffrent types which is why you can do this as well..

Code:

---

char x='d';
double y=3.14;
string s="hello world";
cout<<x;
cout<<y;
cout<<s;

---

Quote:

---

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
}

---

Quote:

---

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;
}

---