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Constructor Error

 
0
  #1
Oct 18th, 2009
My compiler is throwing me this error when I try to make a new one.
I am trying to make it with this

C++ Syntax (Toggle Plain Text) 
  1. string a = "five";
  2.    HashTable<string> *hashy =  new HashTable<string>(a,100);

This is the compiler error
(.text+0x1d3): undefined reference to `HashTable<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::HashTable(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
collect2: ld returned 1 exit status



C++ Syntax (Toggle Plain Text) 
  1. //
  2. #include "hashTable.h"
  3. #include <iostream>
  4. #include <list>
  5. #include <string>
  6. #include <math.h>
  7. #include <iterator>
  8. bool checkforlargeprime (int num);
  9.  
  10. bool checkprime (int nn) {
  11.     if (nn > 100) {
  12.         return checkforlargeprime(nn);
  13.     } else {
  14.         int k=2;
  15.         while (k < nn) {
  16.             int sd = nn%k;
  17.             if ( sd == 0) {
  18.                 return false;
  19.             }
  20.             k++;
  21.         }
  22.     }
  23.     return true;
  24. }
  25. int getNextPrimeNumber (int num) {
  26.     int nam = num+1;
  27.     bool das = true;
  28.     while ( das == true ) {
  29.         if (checkprime(nam))
  30.             das = false;
  31.         else
  32.             nam = nam+1;
  33.     }
  34.     return nam;
  35. }
  36. bool checkforlargeprime (int num) {
  37.     if (num > 100) {
  38.         int sss = ((int)(sqrt((double)num)))+1;
  39.         int pn = 2;
  40.  
  41.         while (pn < sss) {
  42.             if (num%pn == 0) {
  43.                 return false;
  44.             }
  45.             pn = getNextPrimeNumber(pn);
  46.         }
  47.         return true;
  48.     } else {
  49.         return false;
  50.     }
  51. }
  52.  
  53. template <class HashedObj>
  54.         HashTable<HashedObj>::HashTable( const HashedObj & notFound, int size )
  55.           : item( notFound ), theLists( getNextPrimeNumber( size ) )
  56.         {
  57.         }
  58. template <class HashedObj>
  59.         void HashTable<HashedObj>::insert( const HashedObj & x )
  60.         {
  61.             list<HashedObj> &whichList = theLists[hash(x, theLists.size())];
  62.             typename std::list<HashedObj>::iterator itr = whichList.find(x);
  63.  
  64.             if( itr.isPastEnd( ) )
  65.                 whichList.insert( x, whichList.zeroth( ) );
  66.         }
  67. template <class HashedObj>
  68.         void HashTable<HashedObj>::remove(const HashedObj &x )
  69.         {
  70.            theLists[hash( x, theLists.size( ))].remove(x);
  71.         }
  72. template <class HashedObj>
  73.         bool HashTable<HashedObj>::contains(const HashedObj &x )const
  74.         {
  75.            const list<HashedObj> & whichList = theLists[hash(x)];
  76. 		   return find(whichList.begin(),whichList.end(),x)!=whichList.end();
  77.         }
  78.  
  79. template <class HashedObj>
  80.         const HashedObj &HashTable<HashedObj>::find( const HashedObj &x ) const
  81.         {
  82.             typename std::list<HashedObj>::iterator itr;
  83.             itr = theLists[ hash( x, theLists.size( ) ) ].find( x );
  84.             if( itr.isPastEnd( ) )
  85.                 return item;
  86.             else
  87.                 return itr.retrieve( );
  88.         }
  89. template <class HashedObj>
  90.         void HashTable<HashedObj>::makeEmpty( )
  91.         {
  92.             for( int i = 0; i < theLists.size( ); i++ )
  93.                 theLists[ i ].makeEmpty( );
  94.         }
  95.  
  96.         int hash( const string &key, int tableSize)
  97.         {
  98.             int hashVal = 0;
  99. 			for(int i = 0; i<key.length();  i++)
  100. 			hashVal = 37*hashVal+key[i];
  101. 			hashVal %= tableSize;
  102. 			if(hashVal<0)
  103. 			hashVal += tableSize;
  104. 			return hashVal;
  105.         }

C++ Syntax (Toggle Plain Text) 
  1. #ifndef HASHTABLE_H
  2. #define HASHTABLE_H
  3. #include <iostream>
  4. #include <vector>
  5. #include <list>
  6. using namespace std;
  7. template <typename HashedObj>
  8.  class HashTable
  9.  {
  10.  public:
  11.  explicit HashTable( const HashedObj & notFound, int size = 101 );
  12.  HashTable( const HashTable & rhs ): item( rhs.item ), theLists( rhs.theLists ) { }
  13.  void makeEmpty();
  14.  void insert(const HashedObj &x);
  15.  void remove(const HashedObj &x);
  16.  bool contains(const HashedObj &x)const;
  17.  const HashedObj & find( const HashedObj & x ) const;
  18. private:
  19. const HashedObj item;
  20. vector<list<HashedObj> > theLists;
  21. };
  22. template <typename HashedObj>
  23. int hash(const HashedObj &x, int tablesize);
  24. #endif
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0
  #2
Oct 18th, 2009
You need to put the definition and the declaration of a template class
in the same file. 
1) What word becomes shorter if you add a letter to it? [ Solved by : niek_e, Paul Thompson]
2) What does this sequence  equal to :  (.5u - .5a)(.5u-.5b)(.5u-.5c) ...[*]
      [*solved by : murtan]
3) What is the 123456789 prime numer?
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0
  #3
Oct 18th, 2009
firstPerson's answer works and solves the problem BUT for a large classes you might prefer to use explicit instantiation. [which gives the beginner a better idea of what is happening (sometimes)].

so you add a
template class HashTable<std::string>; at the end of HashTable.cpp and then you have told the compiler that you require a particular HashTable type.

Then you don't have to change the includes in anyway, and you don't have a huge .h file to include each time.
experience is the most expensive way to learn anything
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