C++ 需要帮助破译模板元编程宏
我非常想亲自尝试一下，但是我在GCC和Clang上遇到了一个编译错误：C++ 需要帮助破译模板元编程宏,c++,macros,template-meta-programming,C++,Macros,Template Meta Programming,我非常想亲自尝试一下，但是我在GCC和Clang上遇到了一个编译错误： Undefined symbols for architecture x86_64: "foo::_theInfo", referenced from: foo::info() in reflect-eLsDqz.o ld: symbol(s) not found for architecture x86_64 这是代码（直接在博客上发布），我希望沃特先生不介意 /* A simple C++ reflec
Undefined symbols for architecture x86_64:
"foo::_theInfo", referenced from:
foo::info() in reflect-eLsDqz.o
ld: symbol(s) not found for architecture x86_64
/* A simple C++ reflection mark-up library. The strength
of this library is that it is entirely static (all the
reflection information is built without using dynamic
memory allocation), and it is exremely compact, allowing
you to declare the members of a structure right where
that struct is declared, leading to minimal risk of
version mismatch.
This code is placed in the public domain by Jon Watte.
http://www.enchantedage.com/cpp-reflection
Version 2009-04-20
*/
#include <typeinfo>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct TypeBase
{
virtual void Marshal(void *, void const *) const = 0;
virtual void Demarshal(void const *, void *) const = 0;
virtual char const *name() const = 0;
virtual size_t size() const = 0;
};
template<typename T> struct Type : TypeBase
{
static Type<T> instance;
// custom marshaling is handled by template specialization
void Marshal(void *dst, void const *src) const { memcpy(dst, src, sizeof(T)); }
void Demarshal(void const *src, void *dst) const { memcpy(dst, src, sizeof(T)); }
char const *name() const { return typeid(T).name(); }
size_t size() const { return sizeof(T); }
};
template <typename T> T& instance() {
static T t;
return t;
}
template<typename T, typename Q>
TypeBase *get_type(Q T::*mem) {
return &instance<Type<Q> >();
}
struct member_t
{
char const *name;
TypeBase *type;
size_t offset;
};
struct ReflectionBase
{
void ReflectionConstruct();
virtual size_t size() const = 0;
virtual char const *name() const = 0;
virtual size_t memberCount() const = 0;
virtual member_t const *members() const = 0;
};
void ReflectionBase::ReflectionConstruct()
{
// todo: register myself in some table, etc
members();
memberCount();
name();
size();
}
#define MEMBER(x) \
{ #x, get_type(&T::x), (size_t)&((T*)0)->x },
#define RTTI(_type, _mems) \
template<typename T> struct _info : ReflectionBase { \
/* overrides used by ReflectionBase */ \
inline size_t size() const { return sizeof(T); } \
inline char const *name() const { return #_type; } \
inline size_t memberCount() const { size_t cnt; get_members(cnt); return cnt; } \
inline member_t const *members() const { size_t cnt; return get_members(cnt); } \
_info() { ReflectionConstruct(); } \
static inline member_t const *get_members(size_t &cnt) { \
static member_t members[] = { _mems }; \
cnt = sizeof(members) / sizeof(members[0]); \
return members; \
} \
static inline _info<T> &info() { \
return instance<_info<T> >(); \
} \
}; \
inline static member_t const * members() { return _info<_type>::info().members(); } \
static _info<_type> _theInfo; \
inline static _info<_type> &info() { return _theInfo; }
struct foo {
int x, y, z;
RTTI(foo, MEMBER(x) MEMBER(y) MEMBER(z))
};
int main() {
printf("type: %s\n", foo::info().name());
printf("size: %ld\n", foo::info().size());
for (size_t i = 0; i != foo::info().memberCount(); ++i) {
printf(" %s: offset %ld size %ld type %s\n",
foo::info().members()[i].name, foo::info().members()[i].offset,
foo::info().members()[i].type->size(), foo::info().members()[i].type->name());
}
return 0;
}
因此，
static\u info\u theInfoMEMBERinline static\u info&info（）\
{ \
静态信息\
返回信息\
}
\u theInfoinline static _info<_type> &info() \
{ \
static _info<_type> _theInfo; \
return _theInfo; \
}