Why could I not find the class in preprocessor?

Question

This might be very naive, but I am quite confused about the preprocessor of cpp: I defined a header file-- Node.h:

#ifndef NODE_H_
#define NODE_H_

#include<iostream>
class Node{
    friend std::ostream &operator<<(std::ostream &os, const Node & n);
    public:
        Node(const int i = -1);
    private:
        Node * next;
        int value;
    friend class List;

};
#endif

Then I defined the methods in Node.cpp:

#include "Node.h"
using namespace std;

Node::Node(const int i):value(i), next(NULL){}

ostream& operator <<(ostream & os, const Node& n){
    return os<<"value : "<<n.value<<endl;
}

lastly, I have a test.cpp file to check the preprocessor:

#include "Node.h"
//#include <iostream>
using namespace std;

int main(){
    Node * n = new Node;
    cout<<*n;
}

however, when I tried to compile with gcc, I got the following error:

/home/xuan/lib/singleLinkedList/test.cpp:6：‘Node::Node(int)’undefined reference

Answer 1

Given your files, when I run:

$ g++ test.cpp
/tmp/ccM7wRNZ.o:test.cpp:(.text+0x2c): undefined reference to `Node::Node(int)'
/tmp/ccM7wRNZ.o:test.cpp:(.text+0x44): undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, Node const&)'
/usr/lib/gcc/i686-pc-cygwin/4.5.3/../../../../i686-pc-cygwin/bin/ld: /tmp/ccM7wRNZ.o: bad reloc address 0x0 in section `.ctors'
collect2: ld returned 1 exit status

... but if I run:

Simon@R12043 ~/dev/test/cpp
$ g++ test.cpp node.cpp

Simon@R12043 ~/dev/test/cpp
$

Thus, I think you are not including node.cpp among the files to be linked into the project. That is, it is the linker that is not finding the Node class.