Question

class template problem

Answer 1

/file: stack.h
#include <iostream>
using namespace std;
#ifndef STACK_H
#define STACK_H
struct Node {
string x;
Node *next;
};
typedef Node* Stack;
template<class P>
class Stack2{
public:
void push(Stack* pstack, P);
void pop(Stack& stack);
P top(Stack& stack);
bool is_empty(Stack stack);
};
#endif

Answer 2

//file: stack.cpp
#include "stack.h"
template<class P>
void Stack2<P>::push(Stack* pstack, P x){
Node* t;
t=new Node;
t->x=x;
t->next=*pstack;
*pstack=t;
return;
}
template<class P>
P Stack2<P>::top(Stack& stack){
return stack->x;
}
template<class P>
bool Stack2<P>::is_empty(Stack stack){
stack= NULL;
}
template<class P>
void Stack2<P>::pop(Stack& stack){
Node* p;
p=new Node;
p=stack->next;
stack=p;
return;
}

Answer 3

//file:main.cpp
#include <iostream>
#include "stack.h"
#include <vector>
#include <string>
using namespace std;
int main(){
size_t i;
Stack2<P> Stack2;
Stack stack = 0;
string arr[]= {"1","2","3","4"};
vector<string> x(arr, arr +4);
cout<<"Original string vector \n";
for (i=0; i<x.size(); i++){
cout<<x[i]<<", ";}
cout<<endl;
for (i=0; i<x.size(); i++){
Stack2<P>.push(&stack,x[i]);}
cout<<"After using the stack to hold the string in reverse order we get: \n"\
;
Node* p;
p=stack;
while (p !=0){
cout<<p->x<<", ";
p=p->next;
}
cout<<endl;

cout<<"After we use top() we get: \n";
cout<<Stack2<P>.top(stack)<<endl;
cout<<"After we use pop() we get: \n";
Stack2<P>.pop(stack);
Node* w;
w=stack;
while (w !=0){
cout<<w->x<<", ";
w=w->next;
}
cout<<endl;
}

Answer 4

errors:

main.cpp: In function ‘int main()’:
main.cpp:11: error: ‘P’ was not declared in this scope
main.cpp:11: error: template argument 1 is invalid
main.cpp:11: error: invalid type in declaration before ‘;’ token
main.cpp:20: error: expected primary-expression before ‘.’ token
main.cpp:31: error: expected primary-expression before ‘.’ token
main.cpp:33: error: expected primary-expression before ‘.’ token
make: *** [main.o] Error 1

Answer 5

should I declare the template in main? how should i pass that? Im kind of confused

Answer 6

class P replaces the string

Answer 7

i kind of fixed my code but it still doesn't work
http://liveworkspace.org/code/c16eec13056615b082936a4d17882d9c

Answer 8

Are the 3 errors on liveworkspace your only errors at this point?

Answer 9

you know i got it working now at
http://liveworkspace.org/code/a9c412a7e683439dfa35a9363749369d

Answer 10

but on my computer when i use the terminal and compile it i get

Undefined symbols for architecture x86_64:
"Stack2<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::push(Node**, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)", referenced from:
_main in main.o
"Stack2<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::top(Node*&)", referenced from:
_main in main.o
"Stack2<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >::pop(Node*&)", referenced from:
_main in main.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
make: *** [run] Error 1

Answer 11

Reads like you're using a 64-bit compiler reading 32-bit symbols.

Answer 12

what should I do then?

Answer 13

Have you tried compiling with g++?

Answer 14

i made a makefile

Answer 15

run: stack.o main.o
g++ $(FLAGS) -o run stack.o main.o
stack.o: stack.cpp stack.h
g++ $(FLAGS) -c stack.cpp
main.o: main.cpp stack.h
g++ $(FLAGS) -c main.cpp
clean:
rm -f run *.o

Answer 16

hmm, why not try compiling from the commandline with g++, see if it gives you the same errors.

Answer 17

one sec

Answer 18

yeap same problem

Answer 19

A google search revealed: The solution here is that you need to have the definition of the templated function in the header file, not just the declaration. This is a limitation of C++'s templating system.
If you are still getting the same error from the commandline, you might try adding the definition into your header file.

Answer 20

Seems the template is done at compile time rather than linking.

Answer 21

im kind of confused? so how should i give the definition of templated function?

Answer 22

You could create a header file for the template alone and #include it.

Answer 23

thats weird

Answer 24

It is, I cannot find a specific example in my book, however there is one here: http://www.cplusplus.com/forum/general/28838/
Seems this is not an uncommon problem.

Answer 25

but thats what i have in one file is:


//file: stack.h
#include <iostream>
#include <vector>
using namespace std;
#ifndef STACK_H
#define STACK_H
struct Node {
string x;
Node *next;
};
typedef Node* Stack;
template <class P>
class Stack2{
public:
// Stack2(P x);
void push(Stack* pstack, P x);
void pop(Stack& stack);
P top(Stack& stack);
bool is_empty(Stack stack);
private:
vector<P> x;
};
#endif

Answer 26

so should I still seperate the template from the struct node?

Answer 27

You should be able to create a header file with the full definition of your template in it, or one person suggests putting an implementation of the string method that is creating the error into a file you are including.

Answer 28

Can't you just define the functions you are declaring in your header file?

Answer 29

so I should have 2 headers? 1 for the template and other for the struct node

Answer 30

Arguably that appears to be the quickest solution, I cannot find an explicit example of doing this, nor does my book even address issues with a template.

Answer 31

so where should I include template.h in both stack.cpp and main.cpp
?

Answer 32

As I understand the process, yes.

Answer 33

//file:template.h
#include <iostream>
using namespace std;
#ifndef TEMPLATE_H
#define TEMPLATE_H
template <class P>
class Stack2{
public:
// Stack2(P x);
void push(Stack* pstack, P x);
void pop(Stack& stack);
P top(Stack& stack);
bool is_empty(Stack stack);
private:
vector<P> x;
};
#endif

Answer 34

template.h:10: error: ‘Stack’ has not been declared
template.h:11: error: ‘Stack’ has not been declared
template.h:12: error: ‘Stack’ has not been declared
template.h:13: error: ‘Stack’ has not been declared
template.h:15: error: ISO C++ forbids declaration of ‘vector’ with no type
template.h:15: error: expected ‘;’ before ‘<’ token

Answer 35

Well you are including a class Stack that is not defined within the template file.

Answer 36

thats a struct Node

Answer 37

but then I had the same thing previously if i included the struct

Answer 38

Well, a little more research may be required. I have posed the question to a friend of mine that has many years programming experience over me.

Answer 39

Looking at this example though, they include the cpp file in the template.h

// mytemplate.h

#ifndef MYTEMPLATE_H_INCLUDED
#define MYTEMPLATE_H_INCLUDED

template <typename T>
class MyTemplate
{
T AFunction();
};

#include "mytemplate.hpp"

#endif // MYTEMPLATE_H_INCLUDED


// mytemplate.hpp

// looks just like a cpp file, but it isn't
#include "whatever.h"
#include "whateverelseyouneed.h"
#include "mytemplate.h" // superfluous, but harmless

template <typename T>
T MyTemplate<T>::AFunction()
{
// ...
}

Answer 40

thanks a lot for trying to help me, I really appreciate it

Answer 41

My pleasure, it helps me learn too. :)

Answer 42

if I include stack.h in a template.h i get the same error as ld: symbol(s) not found for architecture x86_64. but if I include stack.cpp in a template.h I get some weird long errors

Answer 43

Perhaps you do not need to remove any of your original declarations from the .h file. What do you get if you roll the changes back to the working model from livecode, then simply include that template.h file in your main.cpp. Does it still work on livecode and does it compile from the console?

Answer 44

all the functions acting as a template must be in a header file