Calling a member function of class using objects giving lookup error - c++

Question

I am trying to build plugins in c++ using boost library. helper.h
Header file:
#include <string>
#ifndef HELPER_H
#define HELPER_H
class Helper
{
public:
std::string s;
void helper_new(std::string a);
};
#endif
I defined the member function in a file helper.cpp
#include "helper.h"
namespace boostfs = boost::filesystem;
namespace boostdll = boost::dll;
namespace dll = boost::dll;
// Member Functions()
void Helper::helper_new(std::string a)
{
//int i=0;
std::cout<<"Inside helper_new function!!";
std::cout<<"\n";
std::cout<<a;
std::cout<<"\n";
/*std::ofstream MyFile("/home/deepansh/Desktop/Plugin_example/outputs/helper.txt");
std::cout << "Writing in helper.txt\n"; */
/*for(i=0;i<LONG_MAX;i++)
for(int j=0;j<LONG_MAX;j++);*/
/*MyFile<<a+" ";
MyFile<<i;
MyFile<<"\n";
MyFile.close();*/
std::cout << "Done\n";
}
int main() {
Helper obj;
std::string a;
std::cout<<"Enter string u want to write?";
std::getline(std::cin, a);
obj.s=a;
int choice=1;
std::cout<<"which strat to use? \'1\' or \'2\' ?(default is 1)";
std::cin>>choice;
std::string file="strat"+std::to_string(choice);
boostfs::path lib_path = boostfs::current_path();
boost::filesystem::path p2(std::string(lib_path.string()).append("/plugins/").append(file).append(".so"));
boost::shared_ptr<plugin_api> plugin; // variable to hold a pointer to plugin variable
std::cout << "Loading the plugin" << std::endl;
plugin = dll::import<plugin_api>( // type of imported symbol is located between `<` and `>`
p2, // path to the library and library name
"plugin", // name of the symbol to import
dll::load_mode::append_decorations // makes `libmy_plugin_sum.so` or `my_plugin_sum.dll` from `my_plugin_sum`
);
plugin->handle_task(obj);
std::cout << plugin->print() << std::endl;
}
I called the member function from another file with the help of object of Helper class passed to it as argument(this is compiles as so file) strat1.cpp
#include "../helper.h"
#include <string>
namespace my_namespace {
class strat : public plugin_api {
public:
strat() {
std::cout << "Constructing start" << std::endl;
}
std::string print() const {
return "Hello from strat 1";
}
int handle_task(Helper a) {
//long i=0;
//std::ofstream fout;
//fout.open("/home/deepansh/Desktop/Plugin_example/outputs/strat1.txt");
std::cout<<"Inside strat 1";
std::cout<<"\n";
/*for(i=0;i<LONG_MAX;i++)
for(int j=0;j<LONG_MAX;j++);*/
//fout<<a.s+" ";
//fout<<i;
//fout<<"\n";
//fout.close();
std::cout<<a.s;
std::cout<<"\n";
std::cout<<"going to the helper class function.";
std::string p="Hello man. What's up?";
a.helper_new(p); //error is here
return 0;
}
~strat() {
std::cout << "Destructing strat ;o)" << std::endl;
}
};
I am getting this error ./a.out: symbol lookup error: /home/deepansh/Desktop/Plugin_example/plugins/strat1.so: undefined symbol: _ZN6Helper10helper_newENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
When compiling the code can someone help. compiling:
Convert the plugin library(plugin implementation) to object file by using:
gcc -c -Wall -Werror -fpic strat1.c ../helper.cpp //here -wall and -Werror are for warnings
Then convert the .o files to .so files using(creating shared library from object file) :
gcc -shared -o strat1.so strat1.o
g++-8 helper.cpp -L/usr/lib/x86_64-linux-gnu -lboost_filesystem -L/usr/lib/x86_64-linux-gnu -lboost_system -ldl
when I run the executable a.out the error occurs