类似gflag定义全局变量

我就是我 2023-07-24 02:45 14阅读 0赞

#include <iostream>
    #include <map>
    #include <tuple>
    #include <sstream>
    
    template<class T> T get_from_env(const char* name,const T& _default) { 
      auto s = getenv(name);
      if (s == NULL) return _default;
      std::istringstream is(s);
      T env;
      if (is >> env) { 
        is.peek();
        if (!is) { 
          return env;
        }
      }
      std::cout << "Load" << name << "from env(" << s << ") failed, use default" << _default;
      return _default;
    }
    // 实例化
    template<> std::string get_from_env(const char* name, const std::string& _default) { 
      auto s = getenv(name);
      if (s == NULL) return _default;
      return std::string(s);
    }
    
    #define DECLARE_FLAG(type, name) \ extern "C" type name; \ extern "C" std::string doc_ ## name; \ extern "C" void set_ ## name (const type& t); \ extern "C" type get_ ## name ();
    
    // #define TEA_JIT
    #ifdef TEA_JIT
    #define DEFINE_FLAG(type, name, default, doc) \ DECLARE_FLAG(type, name)
    #define DEFINE_FLAG_WITH_SETTER(type, name, default, doc, setter) \ DECLARE_FLAG(type, name)
    #else
    
    #define DEFINE_FLAG(type, name, default, doc) \ DECLARE_FLAG(type, name); \ type name; \ std::string doc_ ## name = doc; \ void set_ ## name (const type& value) { \ name = value; \ } \ void init_ ## name (const type& value) { \ name = value; \ if (getenv(#name)) { } \ } \ int caller_ ## name = (init_ ## name(get_from_env<type>(#name, default)), 0); \ type get_ ## name () { \ return name; \ }
    
    #define DEFINE_FLAG_WITH_SETTER(type, name, default, doc) \ DECLARE_FLAG(type, name); \ type name; \ std::string doc ## name = doc; \ void setter_ ## name (type value); \ void set_ ## name (const type& value) { \ setter_ ## name (value); \ name = value; \ }; \ void init_ ## name (const type& value) { \ setter_ ## name (value); \ name = value; \ }; \ int caller_ ## name = (init_ ## name (get_from_env<type>(#name, default)), 0);
    #endif
    
    // 在.h 文件声明
    DECLARE_FLAG(int, log_v);
    // 在.cc 文件定义
    DEFINE_FLAG(int, log_v, 1, "");
    int main() { 
      set_log_v(12);
      std::cout << get_log_v() << std::endl;
      return 0;
    }

输出: