How to create objects of a class defined in .so file?

How to create objects of a class defined in .so file?

[Rajesh Lolam]

Hi all,
	Can anyone suggest? How to create objects of a class defined in .so file?
        The steps followed by me are as follows:
1> Created a class in file SharedClass.cpp
2> Created SharedClass.o using the following command
c++ -fPIC -g -c -Wall SharedClass.cpp
3> Created SharedClass.so using the following command
c++ -shared -Wl,soname,SharedClass.so -o SharedClass.so SharedClass.o
4> I've used the test program Test.cpp to load shared object.
=======================================================
SharedClass.h FILE:
#include <iostream.h>
#include <string>
#include <vector>

class SharedClass 
{
    public :
 
        SharedClass();
        ~SharedClass();
 
        int ReadName();
        int DisplayName(int p_iPos);
        int DisplayAll();

    private :
 
        vector<string> m_sNameStore;                                                      
};

=======================================================
Test.cpp FILE:
// System Includes
#include <dlfcn.h>
#include <iostream.h>
#include <string>
#include <vector>
#include "SharedClass.h" 


int main()
{
    cout<<endl<<"********** Start of Shared Object Test **********"<<endl;

    string strLibName = "SharedClass.so";
    cout<<"Calling Dynamic Library '"<<strLibName<<"'...."<<endl;
    void *dlhandle = dlopen(strLibName.c_str(), RTLD_LAZY);
 
    if(!dlhandle)
    {
        cout<<"Error: Unable to point to shared library '"<<strLibName
            <<"'!"<<endl;
        cout<<"********** End of Shared Object Test **********"<<endl<<endl;
        return (0);
    }
    cout<<"Called Dynamic Library '"<<strLibName<<"'."<<endl;
    cout<<"Dynamic Library Handle Created <"<<&dlhandle<<">."<<endl;
 
    string strFuncName = "SharedClass";

    SharedClass (*ptrToFunc)();
    ptrToFunc = (SharedClass (*) ())dlsym(dlhandle, strFuncName.c_str());
    if(ptrToFunc == NULL)
    {
        cout<<"Error: Could not point to function '"<<strFuncName
            <<"'!"<<endl;
        cout<<"********** End of Shared Object Test **********"<<endl<<endl;
        dlclose(dlhandle);
        return (0);
    }
    else
    {
        cout<<"Found Constructor for function '"<<strFuncName<<"'."<<endl;
    }

    ptrToFunc->DisplayAll();
    cout<<".... After Calling DisplayAll() ...."<<endl;
    ptrToFunc->ReadName();
    cout<<".... After Calling ReadName() ...."<<endl;
    
    delete ptrToFunc;

    dlclose(dlhandle);
 
    cout<<"********** End of Shared Object Test **********"<<endl<<endl;
    return (0);
}
=======================================================

The issues are:
1> How to create an object of class (SharedClass)?
2> How to use methods of class (SharedClass?)

Thanks & Regards,
Rajesh

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Re: How to create objects of a class defined in .so file?

[Alexandre Oliva]

On Dec  4, 2000, "Rajesh Lolam" <rajeshlolam@rediffmail.com> wrote:

> 1> How to create an object of class (SharedClass)?

Create an extern "C" function that returns pointers to such objects,
and use dlsym() to obtain a pointer to that function.

> 2> How to use methods of class (SharedClass?)

For this to work, you'll either have to wrap all class methods with
extern "C" functions, and use dlsym to get their addresses, or link
the library explicitly into your application, instead of dlopen()ing
it, so that your code can refer explicitly to the methods.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist    *Please* write to mailing lists, not to me