Re: Helper functions

From:

"Tom Serface" <tom.nospam@camaswood.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 13 Nov 2008 13:07:38 -0800

Message-ID:

<Oqr$cPdRJHA.3488@TK2MSFTNGP03.phx.gbl>

I would create a utility or helper class (named whatever you want) and make
it a singleton so that it only needs to be created once with something like:

CMyHelpers hlp;

hlp.GetInstance()->MyFunction();

Tom

"Jeova Almeida" <jeovaalmeida@yahoo.com> wrote in message
news:eUB$CtYRJHA.4728@TK2MSFTNGP04.phx.gbl...

Hello,

I'm creating some helper functions, like:

CString GetLastErrorMessage(DWORD dwLastError )
{
   LPVOID lpMsgBuf = NULL;

   FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM, NULL, dwLastError,
                                 MAKELANGID(LANG_NEUTRAL,
SUBLANG_DEFAULT), // Default language
                                (LPTSTR) &lpMsgBuf, 0, NULL );

   CString str = (LPCTSTR)lpMsgBuf;

   if( lpMsgBuf != NULL )
      LocalFree(lpMsgBuf);
   return str;
}

I see two options for that:
a) Create a CHelper class with a static GetLastErrorMessage() method
or
b) Create an class-independent, generic function

In previous projects, opting for option b, I coded the functions in a file
named Helpers.h and inserted lots of functions like the one above using
the static keyword, and #including Helpers.h in each file which needed the
functions contained in the helpers.h file. This worked fine.

My questions are:

a) Using the static keyword as stated above and #including the Helper.h
file in, let's say, 20 other classes which depend on the functions
contained in the Helpers.h file will actually include the contents of the
Helpers.h file in all those 20 other classes, swelling the size of the
output file (.exe)?

b) Thinking the question a would be true, I thought of creating a
Helper.cpp file with all the implementation and a Helper.h with all the
declaration, without the static keyword. By doing so, I got the link error
LNK2019 saying the functions are unresolved externals. The Helper.cpp file
is part of the project, and the classes which uses the functions have the
Helper.h #included. Why the functions are considered unresolved?

Jeova