This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 8 years ago.
driver.cc
#include <iostream>
#include "dynStack.h"
using namespace std;
// class definition
int main()
{
dynstack<int> c1;
c1.push(1);
cout<<"hello";
return 0;
}
dynStack.h
#include <iostream>
using namespace std;
template <class T>
class dynstack
{
public:
dynstack();
void push(T data);
};
dynStack.cc
#include "dynStack.h"
template <class T>
dynstack<T>::dynstack()
{
}
template <class T>
void dynstack<T>::push(T data)
{
return data;
}
I'm new to C++. When I run the code, it keeps giving me "undefined reference to 'dynstack::dynstack()' error. I checked include and prototype and couldn't spot the error. Could anyone help me find where I did wrong? Thank you.
Your templated class methods, unless called from within the same .cpp, need to have their implementations in the header, or an inline file included from the header.
Related
This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 1 year ago.
I'm dealing with oop and cannot understand what is wrong. When i try to compile code i get next messsage: undefined reference to `N::my_class::do_something()'. Code is from microsoft: https://learn.microsoft.com/en-us/cpp/cpp/header-files-cpp?view=msvc-160
my_class.h file:
namespace N
{
class my_class
{
public:
void do_something();
};
}
my_class.cpp file:
#include "my_class.h" // header in local directory
#include <iostream> // header in standard library
using namespace N;
using namespace std;
void my_class::do_something()
{
cout << "Doing something!" << endl;
}
my_program.cpp file:
#include "my_class.h"
using namespace N;
int main()
{
my_class mc;
mc.do_something();
return 0;
}
Your code works for me on g++ 8.4.0.
using namespace N; might not enough to declare member function in N for your compiler.
Try to specify the namespace either inline or using a namespace scope in your cpp file.
EDIT: most likely problem. my_class.cpp is not compiled or linked. Check your compile parameters.
This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 2 years ago.
I'm trying to work with deque and template and I wanted to add others files (func.cpp and func.h) so I can declare all my function in these files and then include func.h in main.cpp but I got an some errors:
1. argument list for variable template "display" is missing in main.cpp
2.'deque': undeclared identifier in func.cpp
3.'d': undeclared identifier in func.cpp
here's the main.cpp:
#include <iostream>
#include <algorithm>
#include <deque>
#include "funcr.h"
using namespace std;
int main()
{
deque <int> d1{ 1,5,3,9 };
d1.push_front(2);
display(d1);
return 0;
}
and here's the func.cpp:
#include <iostream>
#include <deque>
template<typename T>
void display(deque<T> d)
{
for (auto e : d)
std::cout << e << std::endl;
}
and there is the func.h:
#pragma once
template<typename T>
void display(deque<T>d);
can someone help me please?
You must define display in func.h, because templated functions must be implemented in header files unless they are explicitly instantiated.
Also, you did not write using namespace std; in func.h (not that you should write it anywhere, especially headers). As a result, you need to write std::deque instead of merely deque.
So func.h should look like the following:
#include <iostream>
#include <deque>
template<typename T>
void display(const std::deque<T>& d)
{
for (auto e : d)
std::cout << e << std::endl;
}
This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 8 years ago.
I am trying to use template but it does not work, the error is : " previously declared here"
this is my Matrix.h file:
#ifndef MATRIX_H
#define MATRIX_H
template <class T>
class Matrix
{
public:
Matrix(int); // default cunstractor
private:
int rows, columns;
};
#include "Matrix.cpp"
#endif
and this is my Matrix.cpp file
#include "Matrix.h"
#include<iostream>
using namespace std;
template <class T>
Matrix<T>::Matrix(int a) // Default constructor
{
columns = a;
rows = 0;
}
and this is the main file:
#include<iostream>
#include "Matrix.h"
using namespace std;
int main()
{
Matrix<int> m1(5);
return 0;
}
I know the code seems very stupid and simple but I wrote much more, I reduce it to very simple code like this and again it doesn't work. Even I removed
#include "Matrix.cpp"
inside the Matrix.h file but still have problem.
Move the content (template definition) of your matrix.cpp file to matrix.h.
This question already has answers here:
Why can templates only be implemented in the header file?
(17 answers)
Closed 9 years ago.
I'm learning C++ and currently experiencing weird problem with Class template.
This is my header file:
#ifndef VECTOR_H
#define VECTOR_H
#include <iostream>
#include <list>
using namespace std;
template <int n>
class Vector {
public:
list<float> coords;
Vector();
Vector(list<float> ncoords);
};
template <int n>
Vector<n>::Vector() {
coords.assign(n, 0.0);
}
#endif
And this is my .cpp file:
#include "vector.h"
#include <list>
using std::ostream;
using namespace std;
template <int n>
Vector<n>::Vector(list<float> ncoords): coords {ncoords}{}
Everything works fine if I do Vector<2> vector;
But linker gives an error if I try to
Vector<20> vector2 { list<float>{} };
Error message
undefined reference to `Vector<20>::Vector(std::list >)'
The question is - how can I solve this problem?
Templates have to be implemented inside header files. This is due to the way linking works. Read the exhaustive answer here carefully. And the next time search before asking.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why can templates only be implemented in the header file?
Undefined reference to function template when used with string (GCC)
C++ templates, undefined reference
I feel I'm missing something linking a C++ project.
I'm not sure if the problem is in the header sources or includes so I made a minimal code sample to demonstrate it.
Main module
minmain.cpp:
#include <stdio.h>
#include <vector>
#include <string>
#include "nodemin.h"
using namespace std;
int main()
{
// Blist libs are included
Node<int>* ndNew = ndNew->Root(2);
return 0;
}
Header file
nodemin.h:
#ifndef NODETEMP_H_
#define NODETEMP_H_
using namespace std;
template<class T>
class Node
{
protected:
Node* m_ndFather;
vector<Node*> m_vecSons;
T m_Content;
Node(Node* ndFather, T Content);
public:
// Creates a node to serve as a root
static Node<T>* Root(T RootTitle);
};
#endif
node module
nodemin.cpp:
#include <iostream>
#include <string.h>
#include <vector>
#include "nodemin.h"
using namespace std;
template <class T>
Node<T>::Node(Node* ndFather, T Content)
{
this->m_ndFather = ndFather;
this->m_Content = Content;
}
template <class T>
Node<T>* Node<T>::Root(T RootTitle) { return(new Node(0, RootTitle)); }
Compile line:
#g++ -Wall -g mainmin.cpp nodemin.cpp
Output:
/tmp/ccMI0eNd.o: In function `main':
/home/******/projects/.../src/Node/mainmin.cpp:11: undefined reference to`Node<int>::Root(int)'
collect2: error: ld returned 1 exit status
I tried compiling into objects but the linking still failed.
Add template class Node<int>; to nodemin.cpp:
#include <iostream>
#include <string.h>
#include <vector>
#include "nodemin.h"
using namespace std;
template <class T>
Node<T>::Node(Node* ndFather, T Content)
{
this->m_ndFather = ndFather;
this->m_Content = Content;
}
template <class T>
Node<T>* Node<T>::Root(T RootTitle) { return(new Node(0, RootTitle)); }
template class Node<int>;