namespaces, linkage error, operator overloading

[jakester]

I am using Visual C++ 2007 to build the code below. I keep getting
linkage error. Could someone please tell me what I am doing wrong? The
code works until I start using namespace for my objects.

Error 1 error LNK2019: unresolved external symbol "class
std::basic_ostr eam<char,struct std::char_trait s<char & __cdecl
graph::operator <<(class std::basic_ostr eam<char,struct
std::char_trait s<char &,class graph::Node &)" (??6graph@@YAAA V?
$basic_ostream@ DU?$char_traits @D@std@@@std@@A AV12@AAVNode@0@ @Z)
referenced in function _main Program.obj

//Node.h
#ifndef NODE_H
#define NODE_H

#include <string>
#include <iostream>

using std::ostream;
using std::string;

namespace graph {
class Node
{
friend ostream &operator<<(ost ream &, Node &);
public:
Node(void);
Node(const string id);
~Node(void);

string getId() const;
void setId(const string &);
private:
string id;
};
}

#endif

//Node.cpp
#include "Node.h"

using graph::Node;

namespace graph {
Node::Node(void )
{
}
Node::Node(cons t string id) {
}

Node::~Node(voi d)
{
}

string Node::getId() const {
return id;
}

void Node::setId(con st string &id) {
this->id = id;
}
}

ostream &operator<<(ost ream &output, Node &node) {
output << node.getId();
return output;
}

//Program.cpp
#include "Node.h"

using graph::Node;
using std::cout;
using std::endl;

int main() {
Node a("a");
Node b("b");

cout << a << " and " << b << endl;
}

[jakester]

On Apr 14, 8:05 pm, "James Kanze" <james.ka...@gm ail.comwrote:

On Apr 14, 11:14 pm, "twomers" <twom...@gmail. comwrote:

[...]

namespace graph {

[...]

ostream &operator<<(ost ream &output, Node &node) {

If this declaration compiles, it's time to change compilers,
fast. It's not, and never has been, legal C++; a member
operator<< takes only one (explicit) parameter.

output << node.getId();
return output;
}
}

--
James Kanze (Gabi Software) email: james.ka...@gma il.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

In my reference book, they say something similar to what you are
saying too (overloading operators as member function should not have 2
operands). I am quite confused. But the code does compile with VC++
and g++. This observation adds much to my confusion.

[James Kanze]

jakester wrote:

On Apr 14, 8:05 pm, "James Kanze" <james.ka...@gm ail.comwrote:

On Apr 14, 11:14 pm, "twomers" <twom...@gmail. comwrote:

[...]

namespace graph {

This is what I misread.

[...]

ostream &operator<<(ost ream &output, Node &node) {

If this declaration compiles, it's time to change compilers,
fast. It's not, and never has been, legal C++; a member
operator<< takes only one (explicit) parameter.

output << node.getId();
return output;
}
}

In my reference book, they say something similar to what you are
saying too (overloading operators as member function should not have 2
operands). I am quite confused. But the code does compile with VC++
and g++. This observation adds much to my confusion.

The problem is simply that I misread the code, and took a
namespace for a class. Overloaded binary operators take one
operand if a member, two if a free function. In namespace
scope, they are free functions, so two operands are in order.

I'm afraid my posting just added to the confusion. Namespaces
and classes have nothing to do with one another.

With regards to your original code: a friend declaration does
*not* declare a member, but rather a function in the enclosing
namespace. Which means, of course, that you have to define the
function in the enclosing namespace; otherwise, you're defining
some other function.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]