Re: Class Destroys itself straight away!

From:

"Alex Blekhman" <tkfx.REMOVE@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 26 Jan 2008 19:34:27 +0200

Message-ID:

<uwD9sGEYIHA.748@TK2MSFTNGP04.phx.gbl>

"Gerry Hickman" wrote:

I have a Class who's constructor accepts an STL wstring, but it
seems to kill itself before it can be used. If I initialize with
int, it works as expected. Here's the sample code and the
output. Note the Destructor is firing twice.

#include "stdafx.h"
using namespace std;

class MyClass
{
public:
MyClass(wstring);
~MyClass(void);
void SayHello(void);
};

int _tmain(int argc, _TCHAR* argv[])
{
wstring wsInput = _T("Passed in String");
MyClass mc = MyClass(wsInput);
// Class kills itself here!

No, a temporary copy is destroyed. The `mc' object is copy
constructed and alive until the end of the scope (i.e., _tmain
function).

Declare a copy constructor for `MyClass', then you'll see that
creation and destruction are symmetric:

class MyClass
{
public:
    MyClass(const MyClass& other);
    ...
};

MyClass::MyClass(const MyClass& other)
{
    wcout << "Copy constructing Class" << endl;
}

Also, MyClass's constructor makes redundant copy of its parameter
since `wsNewString' is passed by value. Pass it by reference to
avoid unnecessary copy:

MyClass::MyClass(const wstring& wsNewString)
{
    ...
}

Alex