c++11 - How to insert a reference to a multimap? -

i have class foo contains multimap unsigned long , reference bar class.

i'm getting error "no matching function call multimap, etc".

what wrong on insert multimap?

[header file]

class foo { public:      foo();      ~foo();      void set(const unsigned long var1, const bar& var2);  private:      struct map_sort     {         bool operator()(const unsigned long& e1, const unsigned long& e2) const         {             return (e2 < e1);         }     };      std::multimap<unsigned long,bar&, map_sort> m_map; }; 

[source file]

void foo::set(const unsigned long var1, const bar& var2) {     m_map.insert(var1,rtime); //<-- error!!!!!!!! } 

you multimap member declared take unsigned long , bar&

std::multimap<unsigned long,bar&, map_sort> m_map; 

while, in source file

void foo::set(const unsigned long var1, const bar& var2) {     m_map.insert(var1,rtime); //var1 const here! (rtime not declared assume meant var2 - const, too) } 

you trying insert const unsigned long , const bar& differ ones declared above (they constant). note const unsigned long isn't issue because copied value so, in fact, multimap keeps own version of variable , "main" 1 can't modified whatsoever.

additionally, check out documentation of multimap's insert method http://www.cplusplus.com/reference/map/multimap/insert/. should use std::pair insert key-value pair:)

solution 1: change method take non-const arguments:

void set(unsigned long var1, bar& var2); 

solution 2: change map contain const values:

std::multimap<const unsigned long, const bar&, map_sort> m_map 

working example:

class foo { public:      foo();      ~foo();      void set(const unsigned long var1, const bar& var2);  private:      struct map_sort     {         bool operator()(const unsigned long& e1, const unsigned long& e2) const         {             return (e2 < e1);         }     };      std::multimap<const unsigned long, const bar&, map_sort> m_map; };  void foo::set(const unsigned long var1, const bar& var2) {     m_map.insert(pair<const unsigned long, const bar&>(var1, var2)); }