Template Class "Sequence/Class Name does not name a type" Error

Question

I'm currently trying to learn templates in C++ and am unable to make sense of this current Error.

I was trying to write a sequence class based out of a code example from the book. I keep getting this error repeatedly.

I am required to write this template modularly. The functions work, but i can't find the source of the errors. I have tried changing name of .cpp file with no success.

This code is nearly identical to that which i found and ran in the book which compiled with no issues.

Here is my Code for header and implementation files.

#ifndef SEQUENCE_H
#define SEQUENCE_H

#include <cstdlib>  // provides size_t

namespace CS3358_FA17_A04_sequenceOfNum
{
   template <class Item>
   class sequence
   {
   public:
      // TYPEDEFS and MEMBER CONSTANTS
      typedef Item value_type;
      typedef size_t size_type;
      static const size_type CAPACITY = 10;
      // CONSTRUCTOR
      sequence();
      // MODIFICATION MEMBER FUNCTIONS
      void start();
      void end();
      void advance();
      void move_back();
      void add(const Item& entry);
      void remove_current();
      // CONSTANT MEMBER FUNCTIONS
      size_type size() const;
      bool is_item() const;
      Item current() const;

   private:
      Item data[CAPACITY];
      size_type used;
      size_type current_index;
   };
}

#include "sequence.hpp"

.HPP File:

namespace CS3358_FA17_A04_sequenceOfNum
{
   template <class Item>
   sequence<Item>::sequence() : used(0), current_index(0) { }

   template <class Item>
   void sequence<Item>::start() { current_index = 0; }

   template <class Item>
   void sequence<Item>::end()
   {
      current_index = (used > 0) ? used - 1 : 0;
   }

   template <class Item>
   void sequence<Item>::advance()
   {
      assert( is_item() );
      ++current_index;
   }

   template <class Item>
   void sequence<Item>::move_back()
   {
      assert( is_item() );
      if (current_index == 0)
         current_index = used;
      else
         --current_index;
   }

   template <class Item>
   void sequence<Item>::add(const Item& entry)
   {
       assert( size() < CAPACITY );

      size_type i;

      if ( ! is_item() )
      {
         if (used > 0)
            for (i = used; i >= 1; --i)
               data[i] = data[i - 1];
         data[0] = entry;
         current_index = 0;
      }
      else
      {
         ++current_index;
         for (i = used; i > current_index; --i)
            data[i] = data[i - 1];
         data[current_index] = entry;
      }
      ++used;
   }

   template <class Item>
   void sequence<Item>::remove_current()
   {
      assert( is_item() );

      size_type i;

      for (i = current_index + 1; i < used; ++i)
         data[i - 1] = data[i];
      --used;
   }

   template <class Item>
   typename sequence<Item>::size_type sequence<Item>::size() const { return used;}

   template <class Item>
   bool sequence<Item>::is_item() const { return (current_index < used); }

   template <class Item>
   typename sequence<Item>::Item sequence<Item>::current() const
   {
      assert( is_item() );

      return data[current_index];
   }
}

Error's Are:

sequence does not name a type -> this occurs in every function

expected initializer before '<' every place a template specifier is used.

I have written many templates before, but i have always defined and implemented in the same file because of compiler and linker issues.

Any help would be much appreciated, here is a complete list of errors and their lines.

g++ -Wall -ansi -pedantic -c sequence.cpp
sequence.cpp:48:4: error: ‘sequence’ does not name a type
    sequence<Item>::sequence() : used(0), current_index(0) { }
    ^
sequence.cpp:51:17: error: expected initializer before ‘<’ token
    void sequence<Item>::start() { current_index = 0; }
                 ^
sequence.cpp:54:17: error: expected initializer before ‘<’ token
    void sequence<Item>::end()
                 ^
sequence.cpp:60:17: error: expected initializer before ‘<’ token
    void sequence<Item>::advance()
                 ^
sequence.cpp:67:17: error: expected initializer before ‘<’ token
    void sequence<Item>::move_back()
                 ^
 sequence.cpp:77:17: error: expected initializer before ‘<’ token
    void sequence<Item>::add(const Item& entry)
                 ^
sequence.cpp:102:17: error: expected initializer before ‘<’ token
    void sequence<Item>::remove_current()
                 ^
sequence.cpp:114:4: error: ‘sequence’ does not name a type
    sequence<Item>::size_type sequence<Item>::size() const { return used;         }
    ^
sequence.cpp:117:17: error: expected initializer before ‘<’ token
    bool sequence<Item>::is_item() const { return (current_index < used);     }
                 ^
sequence.cpp:120:4: error: ‘sequence’ does not name a type
    sequence<Item>::Item sequence<Item>::current() const

Here is Makefile, Also edited my changes in the file extensions.

a4s1: sequence.o sequenceTest.o
    g++ sequence.o sequenceTest.o -o a4s1

sequence.o: sequence.hpp sequence.h
    g++ -Wall -ansi -pedantic -c sequence.hpp

sequenceTest.o: sequenceTest.cpp sequence.hpp sequence.h
    g++ -Wall -ansi -pedantic -c sequenceTest.cpp

test:
    ./a4s1 auto < a4test.in > a4test.out

clean:
    @rm -rf sequence.o sequenceTest.o

cleanall:
    @rm -rf sequence.o sequenceTest.o a4s1

Answer 1

"include the implementation in the header file" doesn't mean #include <sequence.cpp>, it means to actually have everything in sequence.h.

The possible solutions are:

1. Move everything from sequence.cpp to sequence.h and delete sequence.cpp.
2. Rename sequence.cpp to sequence.imp or some other extension and never compile it by itself (remove it from the makefile altogether). It will be compiled in the .cpp file(s) that #include sequence.h (this is probably what is asked of you).
3. Keep sequence.cpp but #include <sequence.h> at the top and use explicit template instantiation.

Answer 2

Templates have to be defined in every compilation unit they're used in, see here. This usually means, that their implementation has to be put inside a header file. If you want to put the implementation in a separat file anyway, you can create an "implementation file" and include it at the end of your header. That seems to be the strategy your professor is recommending.

However, the implementation file may not be treated as separate compilation unit by your built system. It should end in .imp or .hpp or something else but not .cpp.