Config.cpp

#include "Config.h"

const Config& Config::get() {
    return getWriteable();
}

Config& Config::getWriteable() {
    static Config inst;
    return inst;
}

Config::Config() {
    appPath = "";
    docPath = "";
}

Config.h

#pragma once

#include <string>

class Config {
public:
    static const Config& get();
    static Config& getWriteable();
    
    std::string appPath;
    std::string docPath;

private:
    Config();
};

usage.cpp

// to configure a setting
Config::getWriteable().appPath = "c:\myapp\";

// to access a setting
doStuff(Config::get().appPath);