使用cstring类型的模板作为非模板类​​中的数据成员

Question

It's a kind of complicated question.

class Stats {
public:
  Stats();

        // some functions

  QuadraticHashTable<char[4]> teamHash;
};

Due to the requirements, I have to use the template QuadraticHashTable to store c style string and I have to define a QuadraticHashTable type data member in the class Stats, which is not a template.

Anyone can tell me what's wrong with my declaration? The compiler keeps telling me that

"no matching function for call to 'QuadraticHashTable::QuadraticHashTable()' "

BTW, I haven't initialize the data member in constructor for Stat

Thank you.

code for QuadraticHashTable

        template <class HashedObj>
        class QuadraticHashTable
        {
          public:
            explicit QuadraticHashTable( const HashedObj & notFound, int size = 101 );
            QuadraticHashTable( const QuadraticHashTable & rhs )
              : array( rhs.array), ITEM_NOT_FOUND( rhs.ITEM_NOT_FOUND ),
                currentSize( rhs.currentSize ) { }

            const HashedObj & find( const HashedObj & x ) const;

            void makeEmpty( );
            void insert( const HashedObj & x );
            void remove( const HashedObj & x );

            const QuadraticHashTable & operator=( const QuadraticHashTable & rhs );

            enum EntryType { ACTIVE, EMPTY, DELETED };
/////////////////////////////////////////////////////
            friend class Stats;
/////////////////////////////////////////////////////
          private:
            struct HashEntry
            {
                HashedObj element;
                EntryType info;

                HashEntry( const HashedObj & e = HashedObj( ), EntryType i = EMPTY )
                  : element( e ), info( i ) { }
            };

            vector<HashEntry> array;
            int currentSize;
            const HashedObj ITEM_NOT_FOUND;
            bool isPrime( int n ) const;
            int nextPrime( int n ) const;
            bool isActive( int currentPos ) const;
            int findPos( const HashedObj & x ) const;
            int hash( const string & key, int tableSize ) const;
            int hash( int key, int tableSize ) const;
            void rehash( );
        };

Answer 1

That class has no default constructor. Whenever your class has a member that has no default constructor you must explicitly call a non default constructor when you construct your object. If the member has a default (read parameterless) constructor it's called by default.

For example the following recreates your problem

template <class T> 
class Member
{
public:
    Member(T obj)
        :m_obj(obj)
    {

    }
private:
    T m_obj; 
};

class Owner
{
public:
    Owner()
    {
    }

private:
    Member<int> m_member; 
};

In VS I get a slightly clearer error message , but its the same problem the compiler doesn't know how to build a member in this context because you haven't told it how to construct it.

If I change the Owner class to call the appropriate constructor during initialization the compiler now knows how to construct your object.

class Owner
{
public:
    Owner()
        :m_member(4)
    {
    }

private:
    Member<int> m_member; 
};