Experimental Physics and
Industrial Control System

"Mark Rivers" <[email protected]> · Tue, 29 Apr 2008 11:35:00 -0500

Thanks Jinhu! 

That was indeed the problem!  Sorry for not checking that more closely
before I posted.  The problem was that I had the derived class library
listed before the base class library in the xxxAPP_LIB link list.  That
was OK on Windows, but failing on Linux.

Everything works fine now.

Thanks,
Mark

> -----Original Message-----
> From: Song, Jinhu [mailto:[email protected]] 
> Sent: Tuesday, April 29, 2008 11:17 AM
> To: Mark Rivers; [email protected]; [email protected]
> Cc: [email protected]
> Subject: RE: Beginners C++ questions
> 
> Hi Mark,
> 
> I had similar problem when I was trying to create a shared 
> lib (not epics).  It was fixed by checking the order of 
> libraries to link.
> 
> Hope this can give you a hint.
> 
> Jinhu
>  
> 
> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Mark Rivers
> Sent: Tuesday, April 29, 2008 8:23 AM
> To: [email protected]; [email protected]
> Cc: [email protected]
> Subject: FW: Beginners C++ questions
> 
> Folks,
> 
> I'm having a simple problem with linking C++ on Linux that I 
> wonder if you can help with. 
> 
> Here's the problem.
> 
> - I have a C++ base class and a number of derived classes.  
> If the base class is in the same library as the derived 
> classes everything is fine.
> However, if the base class is in a different library from the 
> derived classes, then it compiles fine (because it finds the 
> header file), but it fails at link time.  
> 
>  
> My base class has methods like the following:
>  
> /* Constructor */
> asynParamBase::asynParamBase(const char *portName, int maxAddr, int
> paramTableSize)
>     : maxAddr(maxAddr){ 
> 
> 
> Since that is not declared static, if it were a C function 
> the linker would find it even if it were in a different 
> library.  However, when I try to link this base class which 
> is used by a derived class in another library I get the 
> following error:
>  
> ../NDPluginBase.cpp:454: undefined reference to 
> `asynParamBase::asynParamBase[not-in-charge](char const*, 
> int, int) '../../../lib/linux-x86//libADPlugin.a
> (NDPluginBase.o)(.text+0xfff): In function 
> `NDPluginBase::NDPluginBase[in-charge](char const*, int, int, 
> char const*, int, int, int)':
> 
> However, if I force the linker to include the module that 
> includes the base class source code by adding the following 
> lines to the beginning of
> it:
>  
> /* This is for testing */
> #include <epicsExport.h>
> int asynParamBaseDebug=0;
> epicsExportAddress(int, asynParamBaseDebug);
> 
> and then add this line to the .dbd file:
> 
> variable(asynParamBaseDebug,int)
> 
> then it links OK.
> 
> How do I get the linker to pull in the module with the base 
> class definition without having to force it with that global 
> definition?
> 
> Andrew Johnson suggested putting the keyword epicsShareClass 
> before the class definition.  I tried that, but interestingly 
> it links fine on Windows with or without that keyword, but 
> fails on Linux with or without the keyword.
> 
> Thanks,
> Mark
> 
> 
> 
>  
> 
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System