loops - C++ - Alternative to iterating vector -

i have std::vector<myclass*> (a vector of myclass pointers), , need find particular item in vector. class has getid() function returns unique identifier of class.

if want find class specific id, iterate through vector looking class id, this:

for(std::vector<chunk*>::iterator = chunksrenderlist.begin(); != chunksrenderlist.end(); ++it) {     if((*it)->getid() == id)         return *it; } 

this rather slow because calling code lots of times per second. have tried using std::unordered_map lot slower, , std::map slower again. i'm not sure why slower, maybe it's way used it.

is there container/algorithm can use access particular item without having iterate (that faster iteration)?

if container sorted accoding value of getid() may try using binary search.

class {   size_t m_id; public:   (size_t id) : m_id(id) {}   size_t getid (void) const { return m_id; } };  template<class t1, class t2> struct less_id {   bool operator () (t1 const &lhs, t2 const & cmp)   {     return (lhs->getid() < cmp);   } };  int main (void) {   std::vector<a*> v;   v.push_back(new a(2));   v.push_back(new a(3));   v.push_back(new a(4));   v.push_back(new a(5));    less_id<a*, size_t> cmp;    size_t find_value = 4;   std::vector<a*>::iterator found = std::lower_bound(v.begin(), v.end(), find_value, cmp);   if(found == v.end() || !((*found)->getid() == find_value))   {     // not found   }   else   {     // found     std::cout << "found element: " << (found-v.begin()) << std::endl;   }    (size_t i=0; i<v.size(); ++i) delete v[i];   v.clear(); } 

shows

found element: 2

where a == chunk , v == chunksrenderlist.