Error on Member Initialization

Error on Member Initialization

[Allen Williams]

Hello,

I have the following declared:

class RADCOMMGT_API CradComMgt
    {
public:
    CradComMgt(CLog* Log=NULL);
    ~CradComMgt();

	--- snip ---
	};
/***************************************/

In another file I declare this:

extern CLog Log;                   // <- Note declaration of CLog object

class radApp : public lnDaemon
    {
  public:
    virtual void DaemonInit();

  protected:
    CradComMgt m_MyServer(&Log);	// <- Note initialization
    };
/******************************************/

I get this from the compiler:

g++ -o radApp -D_LINUX -L../Libraries -I../Headers
radApp.cpp -lApp -lLog -lSock -lNetDataSvc -lradComMgt -lradCore
In file included from radApp.cpp:16:
radApp.h:24: error: invalid data member initialization
radApp.h:24: error: (use `=' to initialize static data members)
make: *** [radApp] Error 1

Compilation exited abnormally with code 2 at Fri Sep 12 20:04:53

I have Stroustrup's C++ reference manual and Ellis and Stroustrup's C++
Annotated reference, both of which say this should be a valid form to call
the CradComMgt::CradComMgt(CLog *) constructor.  What am I doing wrong here?

Thanks in Advance,
anw

Re: Error on Member Initialization

[Eljay Love-Jensen]

Hi Allen,

That's not how you initialize a member variable in C++.  (Although it's very close to how you do it in Java.)

You need to put the initialization in your radApp's constructor's initialization list.

e.g.:
radApp::radApp()
: m_MyServer(&Log)
{ }

HTH,
--Eljay

RE: WELCOME to gcc-help@gcc.gnu.org

[Allen Williams]

I can't find the (relatively new) static_cast, dynamic_cast, etc. in the GCC
manual.
Can anyone point me to documentation on how to use these?

TIA,
allen

static_cast, dynamic_cast, etc.

[Allen Williams]

Oops!  Sorry about the original subject line.

> -----Original Message-----
> From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org]On
> Behalf Of Allen Williams
> Sent: Saturday, September 13, 2003 8:40 PM
> To: gcc-help@gcc.gnu.org
> Subject: RE: WELCOME to gcc-help@gcc.gnu.org
> 
> 
> I can't find the (relatively new) static_cast, dynamic_cast, etc. 
> in the GCC
> manual.
> Can anyone point me to documentation on how to use these?
> 
> TIA,
> allen

Re: WELCOME to gcc-help@gcc.gnu.org

[Alexandre Oliva]

On Sep 13, 2003, "Allen Williams" <anw@csunv.com> wrote:

> I can't find the (relatively new) static_cast, dynamic_cast, etc. in the GCC
> manual.

The GCC manual does not document the languages it compiles.  That's
something left for language standardization committees.  Only GCC
extensions or limitations are documented.  Since the Standard C++
new-style casts aren't either, they're not documented in the manual.

> Can anyone point me to documentation on how to use these?

You can get a copy of the ISO C++ Standard directly from the standards
bodies.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                 aoliva@{redhat.com, gcc.gnu.org}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist                Professional serial bug killer

Re: static_cast, dynamic_cast, etc.

[Eljay Love-Jensen]

Hi Allen,

Although not quite as "sacred" as the ISO 14882 standard itself, Stroustrup's "C++ Programming Language" (3rd edition or special edition) is an excellent resource that explains the how's and what's of C++.  A book of knowledge.

And Cline, Lomow, Girou's "C++ FAQs" (2nd edition) is an excellent resource that explains the when's and the why's.  A book of wisdom.

HTH,
--Eljay

Re: Error on Member Initialization

[John Love-Jensen]

Hi Lyle,

>Is there any _real_ difference between these two ways of initializing?

Yes.  The real difference is that the initializer list occurs whether or not
it is explicitly specified.  Putting the initialization code in the
constructor's body MAY incur a performance penalty.  That's a MAY, not a FOR
SURE ... the only way to know for certain is by profiling the optimized
release executable.

In some situations, it is necessary to put more complex resource acquisition
code in the constructor's body.

But, generally speaking, initialization lists are preferable over
initialization via the constructor's body.

The sample code you presented is amenable to the preferred initialization
list solution.

HTH,
--Eljay

RE: Error on Member Initialization

[lrtaylor]

Sorry, I just went back and look at his original code.  I see what he was doing wrong.  However, I'm still curious about my question...

Thanks,
Lyle Taylor
IS Applications

-----Original Message-----
From: lrtaylor 
Sent: Monday, September 15, 2003 11:21 AM
To: eljay@adobe.com; anw@csunv.com; gcc-help@gcc.gnu.org
Subject: RE: Error on Member Initialization

Eljay,

While that's the _preferred_ way to initialize member variables in C++, that's not always possible; sometimes you need to do more complex things to initialize your class (e.g., if you need to initialize variables differently based on certain conditions, retrieve information from a database, etc.).  Is there any _real_ difference between these two ways of initializing?

radApp::radApp()
: m_MyServer(&Log)
{}


radApp ::radApp()
{
  m_MyServer = &Log ;
}

Thanks,
Lyle Taylor
IS Applications

-----Original Message-----
From: Eljay Love-Jensen [mailto:eljay@adobe.com]
Sent: Saturday, September 13, 2003 8:28 AM
To: Allen Williams; gcc-help@gcc.gnu.org
Subject: Re: Error on Member Initialization

Hi Allen,

That's not how you initialize a member variable in C++.  (Although it's very close to how you do it in Java.)

You need to put the initialization in your radApp's constructor's initialization list.

e.g.:
radApp::radApp()
: m_MyServer(&Log)
{ }

HTH,
--Eljay

RE: Error on Member Initialization

[lrtaylor]

Eljay,

While that's the _preferred_ way to initialize member variables in C++, that's not always possible; sometimes you need to do more complex things to initialize your class (e.g., if you need to initialize variables differently based on certain conditions, retrieve information from a database, etc.).  Is there any _real_ difference between these two ways of initializing?

radApp::radApp()
: m_MyServer(&Log)
{}


radApp ::radApp()
{
  m_MyServer = &Log ;
}

Thanks,
Lyle Taylor
IS Applications

-----Original Message-----
From: Eljay Love-Jensen [mailto:eljay@adobe.com]
Sent: Saturday, September 13, 2003 8:28 AM
To: Allen Williams; gcc-help@gcc.gnu.org
Subject: Re: Error on Member Initialization

Hi Allen,

That's not how you initialize a member variable in C++.  (Although it's very close to how you do it in Java.)

You need to put the initialization in your radApp's constructor's initialization list.

e.g.:
radApp::radApp()
: m_MyServer(&Log)
{ }

HTH,
--Eljay