accessing Objects in Multiple Functions C++ - c++

Question

I was seperating my main function from it's loop by creating a new function loop. Now I got the problem that some objects I created in main can't be accessed in loop. Creating multiple function parameters in loop is not an option because it will end in like 30 parameters and more for each Shader and other objects. So I made the objects global:
main.cpp
Shader light("Shaders/light.shader");
Shader depth("Shaders/depth.shader");
Shader.cpp
Shader::Shader(const std::string& filePath)
{
source = parseShader(filePath);
if (shaderGeometry)
ID = createShader(source.vertexSource, source.fragmentSource, source.geometrySource);
else
ID = createShader(source.vertexSource, source.fragmentSource);
use();
}
The problem here is that parsing the file paths outside of a function causes an exception at:
int Shader::createShader(const std::string& vertexShader, const std::string& fragmentShader)
{
program = glCreateProgram(); //<-- HERE
//some further code...
}
The vertexShader and fragmentShader are parsed correctly, so there is no problem.
I guess the exception is thrown because the Shaders need to be created inside a function where the GL function pointers are loaded before.
I tried to play around with extern. But something like this just leaves a compiling error:
global variable
extern Shader light;
extern Shader depth;
in the function
int main()
{
Window wnd(width, height);
Shader light("Shaders/light.shader");
Shader depth("Shaders/depth.shader");
wnd.loop();
//some further code
return 0;
}
Swithing The extern Shader light to the Metod and reversed would end up in the same error from before.
I maybe could access the shader with a getter Method and some kind of Array that safes every vertex, fragment and geometry Shader but maybe there is a more simple way and i just missed something.