c++ - Initializing std::map with an array of std::pairs issue (pointer error?) -

i trying understand how initialize private const std::map properly. have studied this well-known topic none of answers suitable me, because forced use old gcc , boost versions (gcc 4.4, boost 1.41 -> c++11 features limited, boost::asign::map_list_of not compile) and, moreover, don't want use class member function std::map initialization due need of doing outside class @ time of object construction.

however, there overloaded constructor std::map accepts 2 iterators (this thread inspired me too), , workaround:

template <typename arg, typename callback> class callbackselector {     private:         const std::map<arg, callback> mapping;      public:         callbackselector(std::pair<arg, callback> _mapping[]):             mapping(_mapping, _mapping + sizeof(_mapping)/sizeof(std::pair<arg, callback>))             {                 //boost_assert(sizeof _mapping)/(sizeof (std::pair<arg, callback>)) == 2);                 std::cout << "sizeof _mapping " << sizeof _mapping << std::endl;                 std::cout << "sizeof (std::pair<arg, callback>) " << sizeof (std::pair<std::string, boost::function<void(void)> >) << std::endl;             }; };  void pamevent() {}  void defaultevent() {}  int main(int argc, char** argv) {     std::pair<std::string, boost::function<void(void)> > _mapping[] =     {         std::make_pair("pam:", boost::bind(&pamevent)),         std::make_pair("none", boost::bind(&defaultevent))     };     std::cout << "sizeof _mapping " << sizeof _mapping << std::endl;     std::cout << "sizeof (std::pair<arg, callback>) " << sizeof (std::pair<std::string, boost::function<void(void)> >) << std::endl;      callbackselector<std::string, boost::function<void(void)> > selector(_mapping); } 

(the full executable version of example)

if uncomment line boost_assert macro, code not compiled, because size of mapping unequal 2 due error of passing std::pair<std::string, boost::function<void(void)> > _mapping[] callbackselector class constructor. can verify looking @ output:

sizeof _mapping 80                                 //in int main() sizeof (std::pair<arg, callback>) 40  sizeof _mapping 8                                  //in callbackselector constructor sizeof (std::pair<arg, callback>) 40               //the array size has decreased tenfold 

i'll glad if find (apparently?) simple mistake. thank you.

there's no way determine size of array given pointer it. either pass size separate argument:

callbackselector(std::pair<arg, callback> mapping[], size_t size) :     mapping(mapping, mapping + size) 

or infer template parameter:

template <size_t size> callbackselector(std::pair<arg, callback> (&mapping)[size]) :     mapping(mapping, mapping + size) 

or, in c++11 or later, take initializer_list argument

callbackselector(std::initializer_list<std::pair<arg, callback>> mapping) :     mapping(mapping.begin(), mapping.end())  // usage example callbackselector<std::string, boost::function<void(void)> > selector {     {arg1, callback1},      {arg2, callback2} }; 

(note: took liberty of renaming _mapping, reserved name shouldn't have been using).