Question

I have a template class where I want to use objects of that class (along with the parameterized type) inside a map. So far this is the solution that I’ve been able to arrive at:

class IStatMsg;  template <typename T> class ITier { public:      // Methods     ITier(TierType oType) : o_Type(oType){};     virtual ~ITier(){};      typename ITier<T> ParamITier;  // line 60      ITier* Get(T oKey)     {         std::map<T, ParamITier*>::iterator it = map_Tiers.find(oKey);   // line 64          if (it != map_Tiers.end())             return it->second;          return NULL;     }      void Set(T oKey, ITier* pTier)     {         map_Tiers.insert(pair<T, ParamITier*>(oKey, pTier)); // line 74     }      TierType GetType() { return o_Type; }  protected:     // Methods      // Attributes     std::map<T, ParamITier*> map_Tiers;  // line 83     TierType o_Type;  private:     // Methods      // Attributes }; 

But when I try to compile this code I get a long list of errors:

/home/gayanm/street/src/QueryServer_NEW/ITier.h:60: error: expected nested-name-specifier /home/gayanm/street/src/QueryServer_NEW/ITier.h:60: error: ITier<T>' specified as declarator-id /home/gayanm/street/src/QueryServer_NEW/ITier.h:60: error: perhaps you wantITier’ for a constructor /home/gayanm/street/src/QueryServer_NEW/ITier.h:60: error: two or more data types in declaration of ITier<T>' /home/gayanm/street/src/QueryServer_NEW/ITier.h:60: error: expected;’ before ‘ParamITier’ /home/gayanm/street/src/QueryServer_NEW/ITier.h:83: error: ParamITier' was not declared in this scope /home/gayanm/street/src/QueryServer_NEW/ITier.h:83: error: template argument 2 is invalid /home/gayanm/street/src/QueryServer_NEW/ITier.h:83: error: template argument 4 is invalid /home/gayanm/street/src/QueryServer_NEW/ITier.h:83: error: ISO C++ forbids declaration of map_Tiers’ with no type /home/gayanm/street/src/QueryServer_NEW/ITier.h: In member function ITier<T>* ITier<T>::Get(T)': /home/gayanm/street/src/QueryServer_NEW/ITier.h:64: error:ParamITier’ undeclared (first use this function) /home/gayanm/street/src/QueryServer_NEW/ITier.h:64: error: (Each undeclared identifier is reported only once for each function it appears in.) /home/gayanm/street/src/QueryServer_NEW/ITier.h:64: error: template argument 2 is invalid /home/gayanm/street/src/QueryServer_NEW/ITier.h:64: error: template argument 4 is invalid /home/gayanm/street/src/QueryServer_NEW/ITier.h:64: error: expected ;' before '::' token /home/gayanm/street/src/QueryServer_NEW/ITier.h:66: error:it’ undeclared (first use this function) /home/gayanm/street/src/QueryServer_NEW/ITier.h:66: error: request for member end' in ((ITier)this)->ITier::map_Tiers’, which is of non-class type int' /home/gayanm/street/src/QueryServer_NEW/ITier.h: In member functionvoid ITier::Set(T, ITier)’: /home/gayanm/street/src/QueryServer_NEW/ITier.h:74: error: request for member insert' in ((ITier*)this)->ITier::map_Tiers’, which is of non-class type int' /home/gayanm/street/src/QueryServer_NEW/ITier.h:74: error:pair’ undeclared (first use this function) /home/gayanm/street/src/QueryServer_NEW/ITier.h:74: error: expected primary-expression before ‘,’ token /home/gayanm/street/src/QueryServer_NEW/ITier.h:74: error: ParamITier' undeclared (first use this function) /home/gayanm/street/src/QueryServer_NEW/ITier.h:74: error: expected primary-expression before '>' token /home/gayanm/street/src/QueryServer_NEW/ITier.h: At global scope: /home/gayanm/street/src/QueryServer_NEW/ITier.h:93: error: baseITier’ with only non-default constructor in class without a constructor /home/gayanm/street/src/QueryServer_NEW/ITier.h:109: error: expected class-name before ‘{‘ token

Could you please point out how to fix these?

Thank You.

Answer 1

Line 60 does not access a depending name. What you use is ITier<T> of which the compiler knows it’s a template given an argument. Instead of typename you want to use typedef 😉

Line 64 does access the depending name iterator which is a type-name, so you have to put typename before std::map. I put the two disambiguations, template and typename on this answer: Disambiguations of dependent names.

Line 74 would be right, if you fix the bug in Line 60, as far as i can see.

Line 83 is alright in itself as far as i can see.