C++给定一个字符串列表，如何从一个类中获取相应的变量地址

Question

我有课

class MyClass{
public:
   int var_x;
   int var_y;
   int var_z;
}

然后是一个file.txt:

var_y
var_z

主要是想获取file.txt中每个变量的地址:

int main()
{
     MyClass *obj;
     obj = new MyClass();
     std::vector<std::string>> varList = readFile("file.txt");

     // I need generic code that would do the following:
     // But the class can have any number (or named) variables
     // And the text file can have any subset of the variables
     std::cout << "var_y  " << &(obj->var_y) << std::endl;
     std::cout << "var_y  " << &(obj->var_z) << std::endl;

     delete obj;
     return 0;

     // Pseudo code would be
     for var in varList:
         addr = get_addr_from_string(var)
}

Answer 1

using Gettor = std::function< std::any(void*) > get_ptr;

template<class T>
struct ReflectedClass {
  static std::unordered_map<std::string, Gettor> members;
  template<class U>
  static U* get( T* t, const char* name ) {
    auto it = members.find(name);
    if (it == members.end()) return nullptr;
    std::any a = it->second( t );
    U** ptr = std::any_cast<U*>(&a);
    if (!ptr) return nullptr;
    return *ptr;
  }
};

#define TO_STR2(X) ##X
#define TO_STR(X) TO_STR2(X)
#define REFLECTED_MEMBER( CLASS, NAME ) \
  ReflectedClass<CLASS>::members[ TO_STR(NAME) ] = \
  []( void* ptr )->std::any { \
    return std::addressof( (CLASS*)(ptr)->NAME ); \
  }

然后简单地做

REFLECTED_MEMBER(MyClass, var_x )
REFLECTED_MEMBER(MyClass, var_y )
REFLECTED_MEMBER(MyClass, var_z )

你可以调用

MyClass foo;
int* ptr = ReflectedClass<MyClass>::get<int>( &foo, "var_x" );

它返回指向 foo.var_x 的指针。

这是个坏主意，不要这样做。