arrays - Classic Linker Mach error in C++ -

i don't know c++ , i'm teaching myself adt's , data structures. unfortunately every time need compile code classic xcode error: mach link error. tend understand these errors when they're in objective-c (because means i'm missing file). made sure add file target avoid issue, didn't seem work. neither did classic turn xcode on , off trick.

below error , code:

undefined symbols architecture x86_64:   "arraybag<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >::getindexof(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) const", referenced from:       arraybag<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >::remove(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in main.o   "arraybag<int>::getindexof(int const&) const", referenced from:       arraybag<int>::remove(int const&) in main.o ld: symbol(s) not found architecture x86_64 clang: error: linker command failed exit code 1 (use -v see invocation)  #ifndef _array_bag #define _array_bag #include "baginterface.h" #include <vector>   template<class itemtype> class arraybag : public baginterface<itemtype> { private:     static const int default_capacity = 24; // bag size bit bigger allow                                             // adding bags.     itemtype items[default_capacity];      // array of bag items     int itemcount;                         // current count of bag items     int maxitems;                          // max capacity of bag      // returns either index of element in array items     // contains given target or -1, if array not contain     // target.     int getindexof(const itemtype& target) const;  public:     arraybag();     int getcurrentsize() const;     bool isempty() const;     bool add(const itemtype& newentry);     void clear();     bool remove(const itemtype& anentry);     bool contains(const itemtype& target) const;     int getfrequencyof(const itemtype& anentry) const;     arraybag<string> merge(arraybag<string> a, arraybag<string> b);     std::vector<itemtype> tovector() const;      #include "arraybag.h" #include <cstddef>  template<class itemtype> arraybag<itemtype>::arraybag(): itemcount(0), maxitems(default_capacity) { }  // end default constructor  template<class itemtype> int arraybag<itemtype>::getcurrentsize() const {     return itemcount; }  // end getcurrentsize  template<class itemtype> bool arraybag<itemtype>::isempty() const {     return itemcount == 0; }  // end isempty  template<class itemtype> bool arraybag<itemtype>::add(const itemtype& newentry) {     bool hasroomtoadd = (itemcount < maxitems);     if (hasroomtoadd)     {         items[itemcount] = newentry;         itemcount++;     }  // end if      return hasroomtoadd; }  // end add  template<class itemtype> void arraybag<itemtype>::clear() {     itemcount = 0; }  // end clear  template<class itemtype> bool arraybag<itemtype>::remove(const itemtype& anentry) {     int locatedindex = getindexof(anentry);     bool canremoveitem = !isempty() && (locatedindex > -1);     if (canremoveitem)     {         itemcount--;         items[locatedindex]=items[itemcount];     }//end if     return canremoveitem; } //end remove  template<class itemtype> bool arraybag<itemtype>::contains(const itemtype& anentry) const {     bool found = false;     int curindex = 0; //current array index     while(!found && (curindex < itemcount))     {         if(anentry == items[curindex])         {             found = true;         } //end if          curindex++; //increment next entry     } //end while     return found; }  template<class itemtype> int arraybag<itemtype>::getfrequencyof(const itemtype& anentry) const {     int frequency = 0;     int curindex = 0; //current index array     while(curindex < itemcount)     {         if (items[curindex] == anentry)         {             frequency++;         } //end if          curindex++; //incremenet next entry     } //end while     return frequency; } //end getfrequencyof   template<class itemtype> vector<itemtype> arraybag<itemtype>::tovector() const {     vector<itemtype> bagcontents;     (int = 0; < itemcount; i++)         bagcontents.push_back(items[i]);      return bagcontents; }  // end tovector  #include <iostream> #include <string> #include "arraybag.h" #include "arraybag.cpp"  using namespace std;  void displaybag(arraybag<string>& bag) {     cout << "the bag contains " << bag.getcurrentsize()     << " items:" << endl;     vector<string> bagitems = bag.tovector();     int numberofentries = (int)bagitems.size();     (int = 0; < numberofentries; i++)     {         cout << bagitems[i] << " ";     }  // end     cout << endl << endl; }  // end displaybag  void displaybag(arraybag<int>& bag) {     cout << "the bag contains " << bag.getcurrentsize()     << " items:" << endl;     vector<int> bagitems = bag.tovector();     int numberofentries = (int)bagitems.size();     (int = 0; < numberofentries; i++)     {         cout << bagitems[i] << " ";     }  // end     cout << endl << endl; }  // end displaybag  int sumofbag(arraybag<int>& abag) {     int sum=0;     vector<int> abagvector = abag.tovector();     int numberofentries = (int) abagvector.size();     (int = 0; < numberofentries; i++)     {         sum += abagvector[i];     }     //cout << "the sum of bag " << sum << endl;     return sum; }  void bagtester(arraybag<string>& bag) {     cout << "isempty: returns " << bag.isempty()     << "; should 1 (true)" << endl;     displaybag(bag);      string items[] = {"one", "two", "three", "four", "five", "one"};     cout << "add 6 items bag: " << endl;     (int = 0; < 6; i++)     {         bag.add(items[i]);     }  // end      displaybag(bag);      cout << "isempty: returns " << bag.isempty()     << "; should 0 (false)" << endl;      cout << "getcurrentsize: returns " << bag.getcurrentsize()     << "; should 6" << endl;      cout << "try add entry: add(\"extra\") returns "     << bag.add("extra") << endl;     displaybag(bag); } // end bagtester   int main() {     arraybag<string> bag;     cout << "testing array-based bag:" << endl;     cout << "the initial bag empty." << endl;     bagtester(bag);     arraybag<string> bag_of_strings1;     string items[] = {"tom","dick","harry"};     (int i=0; i<3; i++) {bag_of_strings1.add(items[i]);}     displaybag(bag_of_strings1);     arraybag<string> bag_of_strings2;     string new_items[] = {"now","is","the","time","for","all"};     for(int i=0; i<6; i++){         bag_of_strings2.add(new_items[i]);     }     displaybag(bag_of_strings2);     //arraybag<string> newbag=merge(bag_of_strings1,bag_of_strings2);      //displaybag(newbag);      arraybag<int> bag_of_ints;     int array_of_ints[]={6,7,85,9,12,15};     (int i=0;i<6;i++){         bag_of_ints.add(array_of_ints[i]);     }     displaybag(bag_of_ints);     cout<<sumofbag(bag_of_ints)<<endl;      return 0; } // end main 

the linker telling there no implementation arraybag::getindexof. implementation missing code dump. try adding this:

int arraybag<itemtype>::getindexof(const itemtype& target) const {     // todo     return 0; } 

unlike normal classes, template classes should defined in single header file without corresponding .cpp file.