Forward Declaration

[Jon Dahl <jd...@yahoo.com>]

Hello,

I'm wondering if it is possible to use forward declaration with log4cxx classes in a class header file. I would like to exclude the log4cxx headers files in my header files if possible and include the log4cxx header files in my cpp(source) files.

Should this work?

// Test.hpp
namespace log4cxx {
class LoggerPtr;
}

class Test {
private:
    static log4cxx:LoggerPtr    _logger;

public:
    Test();
};

//Test.cpp

#include <log4cxx/logger.h>

using namespace log4cxx;

LoggerPtr Test::_logger(Logger::getRootLogger());

Test::Test() {
}

// end test.cpp

Thanks,

-jd-



      

Re: Forward Declaration

[Curt Arnold <ca...@apache.org>]

On Sep 12, 2008, at 12:00 PM, Jon Dahl wrote:

> Hello,
>
> I'm wondering if it is possible to use forward declaration with  
> log4cxx classes in a class header file. I would like to exclude the  
> log4cxx headers files in my header files if possible and include the  
> log4cxx header files in my cpp(source) files.
>
> Should this work?
>

No.  LoggerPtr is a template expansion and you'd need at least the  
template definition incorporate it in a header file.  However, you may  
want to consider not having a LoggerPtr in your class definition at  
all, but just have it in your implementation.  Something like:

myfoo.cpp

#include <log4cxx/logger.h>

//  anonymous namespace, members are visible only in this compilation  
unit
//   like static but better
//
namespace {
log4cxx::LoggerPtr logger(log4cxx::Logger::getRootLogger());
}

void Foo::someFunction() {
     LOG4CXX_INFO(logger, "Hello, World");
}

RE: Forward Declaration

[re...@rubixinfotech.com]

Stephen - you're right... if the class itself is used, the compiler won't 
know how to construct it... if it is a ptr, it won't complain.

Renny Koshy
President & CEO

--------------------------------------------
Rubix Information Technologies, Inc.
www.rubixinfotech.com



"Stephen Bartnikowski" <sb...@barkinglizards.com> 
09/12/2008 01:16 PM
Please respond to
"Log4CXX User" <lo...@logging.apache.org>


To
"'Log4CXX User'" <lo...@logging.apache.org>
cc

Subject
RE: Forward Declaration






Somebody correct me if I'm wrong, but I don't think it will. In Test.hpp, 
the compiler doesn't know what type LoggerPtr is. Since you're referring 
to that type directly rather than by a pointer, the compiler needs to know 
the full details. It doesn't know that in reality it's a pointer type 
defined elsewhere. If for example, your code instead read:
 
...
class Test {
private:
    static log4cxx::LoggerPtr* _logger;
...
 
then the compiler wouldn't complain.
 
- Stephen

From: Jon Dahl [mailto:jdahl1972@yahoo.com] 
Sent: Friday, September 12, 2008 12:01 PM
To: log4cxx-user@logging.apache.org
Subject: Forward Declaration

Hello,

I'm wondering if it is possible to use forward declaration with log4cxx 
classes in a class header file. I would like to exclude the log4cxx 
headers files in my header files if possible and include the log4cxx 
header files in my cpp(source) files.

Should this work?

// Test.hpp
namespace log4cxx {
class LoggerPtr;
}

class Test {
private:
    static log4cxx:LoggerPtr    _logger;

public:
    Test();
};

//Test.cpp

#include <log4cxx/logger.h>

using namespace log4cxx;

LoggerPtr Test::_logger(Logger::getRootLogger());

Test::Test() {
}

// end test.cpp

Thanks,

-jd-

RE: Forward Declaration

[Stephen Bartnikowski <sb...@barkinglizards.com>]

Somebody correct me if I'm wrong, but I don't think it will. In Test.hpp,
the compiler doesn't know what type LoggerPtr is. Since you're referring to
that type directly rather than by a pointer, the compiler needs to know the
full details. It doesn't know that in reality it's a pointer type defined
elsewhere. If for example, your code instead read:
 
...
class Test {
private:
    static log4cxx::LoggerPtr* _logger;
...
 
then the compiler wouldn't complain.
 
- Stephen


  _____  

From: Jon Dahl [mailto:jdahl1972@yahoo.com] 
Sent: Friday, September 12, 2008 12:01 PM
To: log4cxx-user@logging.apache.org
Subject: Forward Declaration


Hello,

I'm wondering if it is possible to use forward declaration with log4cxx
classes in a class header file. I would like to exclude the log4cxx headers
files in my header files if possible and include the log4cxx header files in
my cpp(source) files.

Should this work?

// Test.hpp
namespace log4cxx {
class LoggerPtr;
}

class Test {
private:
    static log4cxx:LoggerPtr    _logger;

public:
    Test();
};

//Test.cpp

#include <log4cxx/logger.h>

using namespace log4cxx;

LoggerPtr Test::_logger(Logger::getRootLogger());

Test::Test() {
}

// end test.cpp

Thanks,

-jd-