Question

I am working on getting a library to build in linux. This builds and works in Windows, but on Linux I am getting an unresolved symbol in our library when consuming the static lib. The code appears as follows:

class MyClass : public AnotherClassRefCounded
{
public:
  static bool queryInstance(MyClass **ppmyClass);
};

Inside the .cpp file for this class I have:

#include "stdafx.h"
#include "MyClass.h"

MyClass* MyClass::m_pInstance = NULL;

bool MyClass::queryInstance(MyClass **myClass)
{
  if(m_pInstance == NULL)
  {
    m_pInstance = new MyClass();
    m_pInstance->incRef(); 
  }

  m_pInstance->incRef();
  *myClass = m_pInstance;
  return true;
}

Now when running nm -Cu on libMyLib.a I get the following output:

[matt6809@hogganz400 libDebug]$ nm -Cu libMappingd.a | grep queryInstance
                 U AFewMoreScopes::MyClass::queryInstance(AFewMoreScopes::MyClass**)

My system info is:

[matt6809@hogganz400 libDebug]$ cat /etc/redhat-release ; gcc --version
Red Hat Enterprise Linux Server release 6.1 (Santiago)
gcc (GCC) 4.4.5 20110214 (Red Hat 4.4.5-6)
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

For copyright reasons I cannot post the identical code. I have reproduced the code to the best of my abilities. If you feel I am missing any info please don’t hesitate to ask for it.

---

UPDATE

Example of build:

…

g++ -c -include Mappingd -pipe -w -g -fPIC -Wall -W <DEFINE FLAGS> <INCLUDE FLAGS> -o MyClass.o MyClass.cpp

…

ar cqs libMappingd.a <all object files>

---

UPDATE 0

This is very interesting. Inside the object file for “MyClass” the symbol is not undefied:

MyClass.o:
                 <My Symbol Not Undefined>

However if you go to another one of the object files:

<Other Object>.o:
                 ...
                 U Scope::MyClass::queryInstance(Socpe::MyClass**)

---

UPDATE1

g++ -c -include Mappingd -pipe -w -g -fPIC -Wall -W -DLINUXx86 <DEFINE FLAGS> <INCLUDE FLAGS> -o MyClass.o MyClass.cpp
g++ -c -include Mappingd -pipe -w -g -fPIC -Wall -W -DLINUXx86 <DEFINE FLAGS> <INCLUDE FLAGS> -o OtherClass.o OtherClass.cpp
rm -f libMappingd.a
ar cqs libMappingd.a <Other Objects> MyClass.o OtherClass.o

and

g++ -c -include Mappingd -pipe -w -g -fPIC -Wall -W -DLINUXx86 <DEFINE FLAGS> <INCLUDE FLAGS> -o OtherClass.o OtherClass.cpp
g++ -c -include Mappingd -pipe -w -g -fPIC -Wall -W -DLINUXx86 <DEFINE FLAGS> <INCLUDE FLAGS> -o MyClass.o MyClass.cpp
rm -f libMappingd.a
ar cqs libMappingd.a <Other Objects> OtherClass.o MyClass.o

Make no difference I still get undefined symbol in the other library.

Answer 1

After much research, I discovered that the archiver on RHEL 6.1 has a bug in it. I stopped trying to pull in the static libs directly into the shared dynamic library, and instead I unpacked the static libs, and pulled the corresponding object files directly into the .so file. I now have 0 undefined symbols in our library apart from the ones that I am not statically linking against.