C++ objcopy to make class method weak - c++

Question

I have this header file:
weather.h
#ifndef _WEATHER_H_
#define _WEATHER_H_
#include <string>
using namespace std;
class Weather {
private:
int temp;
public:
Weather();
string announce();
};
#endif
When I compile the related source file, I want to make announce and Weather (the default constructor) weak during compile time.
To do so, the flow looks something like:
g++ -std=c++11 -g -Wall -c weather.cpp
objcopy --weaken-symbol=announce --weaken-symbol=Weather weather.o weather.o
However, when I then compile another version of weather without the weakening? I still get a duplicate symbol error.
I know --weaken exists, but this is just a sample and I do not want to blanket weaken every method in the class.

Answer 1

Weakening the symbols in the one file and linking all the objects together works for me. Make sure you are relinking all the objects (including all constructors).
weather1.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather");
}
weather2.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather 2");
}
build.sh
g++ weather1.cpp -c -o weather1.o
g++ weather2.cpp -c -o weather2.o
g++ test.cpp -c -o test.o
objcopy --weaken-symbol=_ZN7Weather8announceEv --weaken-symbol=_ZN7WeatherC2Ev --weaken-symbol=_ZN7WeatherC1Ev weather2.o weather2.o
g++ *.o -o test.out
Depending on whether I weaken weather1.o or weather2.o, I see different outputs from my test main function:
int main()
{
Weather w;
std::cout << w.announce() << "\n";
return 0;
}