Using template value inside nested class

Question

I have the following class definition:

template <int B>
class SparseBitvector
{
    typedef typename std::vector<std::bitset<B>> BitsetVector;

public:
    class iterator: public std::iterator<...>
    {
        public:
            explicit iterator(..., BitsetVector::iterator* _chunksIt, ...) {...}
    }
}

At compilation I get this error:

/project/powerset/src/powerset/sparse_bitvector.h:96:125: error: 'std::BitsetVector<std::bitset<(long unsigned int)B>, std::allocator<std::bitset<(long unsigned int)B> > >::iterator' is not a type
         explicit iterator(SortedStaticSet<EHRule> *_offsets, std::vector<std::bitset<B>> *_chunks, SetElement* _offssetsIt, BitsetVector::iterator* _chunksIt, int _indInBitset)

Is it allowed to use template value inside a nested class?

If not, is there some other error I am making?

Please post a minimal reproducible example. The iterator<...> thing is not valid C++ code. — n. m. could be an AI
– n. m. could be an AI, Commented Jun 6, 2020 at 12:09

JeJo · Accepted Answer · 2020-06-06 12:09:35Z

3

You need to use typename keyword for depended types. Here for example

typename BitsetVector::iterator* _chunksIt
//^^^^^^

Secondly, there is no typename needed for the template type alias

typedef std::vector<std::bitset<B>> BitsetVector;
// or better use
// using BitsetVector = std::vector<std::bitset<B>>;

The minimal example for the above have considered as follows:

#include <vector>
#include <iterator>
#include <bitset>

template <int B>
class SparseBitvector
{
   typedef std::vector<std::bitset<B>> BitsetVector;

public:
   class iterator : public std::iterator<std::input_iterator_tag, BitsetVector>
   {
   public:
      explicit iterator(std::input_iterator_tag, BitsetVector, typename BitsetVector::iterator* _chunksIt)
      {
      }
   };
};

answered Jun 6, 2020 at 12:09

JeJo

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