Expected function body after function declarator

when I build my project with target "mac", I got a complile error as follow:

#ifndef __LUA_PBC_EXTRA_H_

#define __LUA_PBC_EXTRA_H_

#if defined(_USRDLL)

#define LUA_EXTENSIONS_DLL __declspec(dllexport)

#else / use a DLL library */

#define LUA_EXTENSIONS_DLL

#endif

#if __cplusplus

extern "C" {

#endif

#include "lauxlib.h"

int LUA_EXTENSIONS_DLL luaopen_protobuf_c(lua_State *L); // got compile error here : Expected function body after function declarator

#if __cplusplus

}

#endif

#endif / __LUA_EXTRA_H_ */