NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/14263

Text File | 1996-08-05 | 3.2 KB | 86 lines

Path: news.sprintlink.net!datalytics!usenet
From: Rob Stewart <[e-mail]>
Newsgroups: comp.lang.c++
Subject: Re: HELP: Code in Header Files
Date: Fri, 29 Mar 1996 13:02:00 -0500
Organization: Datalytics, Inc
Message-ID: <[e-mail]>
References: <4jakhm$[e-mail]>
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[e-mail] wrote:
>
> I have a problem understanding how header files work.  If it matters I am
> using Borland C++ 4.5...
>
> The problem is I defined a header file   string.h  in this I declared a
> string class.  If I put the actual code to the functions in this class
> into the header file, the compiler does not like it.  I looked at other
> .h files and saw they did not do it this way.
>
> So then I tried writing the actual code into string.cpp and compiling
> that with and #include "string.h".
>
> It worked but my code for my program does not recognize the functions.
> It says I did not code them yet.
>
> It finds the headers just fine but not the actual code.
>
> ie:
>
> #include "string.h"
>
> void main(void)
> {
>     String blah("hello world");
> }
>
> the error will say something like
>
> Undefined Symbol String::~String() in module STEST.CPP
>
> and it goes on to list the rest of the function not "defined".
>
> Please help...

You have to link with the object code generated for your string
class.  There are several approaches to doing that.  The
simplest is to add string.cpp to your project.  The compiler
will compile that code too, and the linker will then add that
object code to your application.

While that was the simplest approach, it doesn't allow you to
reuse string.cpp reliably.  You could add string.cpp to each of
your applications, but you would probably do so by making a
copy.  With this approach, you'd end up with many copies of
string.cpp (and probably string.h too), so any changes you make
must be done to every copy.

The first approach to reusing the code is to put it into a
static library, a .LIB file.  You create a new project in BC to
generate a static library, make string.cpp the one file in the
project, then build your library.  (You would probably name the
output string.lib.)  Now, if you return to your application's
project, tell the linker to link with string.lib (be sure
string.cpp is not part of the project).  The linker will now
locate string.lib, scan it for object files with the necessary
code, and link that code into your application.

You can get even fancier by building a DLL.  A dynamic link
library is essentially the same as a static library, except the
"linking" stuff doesn't occur until load time.  When the OS
loads your application, it will find references to the DLL and
will patch stub calls, to the functions in the DLL, with the
correct address within the DLL.  Once the loader is finished,
you'll have a runtime configuration essentially the same as you
got at link time with a static library.  The DLL code
essentially becomes part of your application while it runs.

--
Robert Stewart        | My opinions are usually my own.
Datalytics, Inc.    | [e-mail]