C++ linker error - c++

Question

I'm new to C++ and need some help with namespaces.
Following are my 4 files:
node.h <--class interface
node.cpp <--implementation
testNodeFunctions.cpp
testNodeMain.cpp
//node.h
---------------------------------
#include <iostream>
using namespace std;
namespace namespaceName{
class Node {
private:
int data;
public:
void setData( int x);
int getData();
};
//and some more functions
}
//node.cpp
-------------------------------------
#include <iostream>
#include "node.h"
using namespace std;
namespace namespaceName {
//provides implementation of the memeber functions
int Node::getData() const{
return data;
}
void Node::setData(int x){
data=x;
}
}//namespace
//testNodeFunctions.cpp
-------------------------------------
#include <iostream>
#include "Node.h"
using namespace std;
using namespace namespaceName;
void showData(){
//creates a Node object and prints some stuff
Node a=37;
cout<<a.getValue()<<endl;
}
//testNodeMain.cpp
----------------------------------------------
#include <iostream>
#include "Node.h"
void showData();
int main(){
//calls methods from testNodeFunctions
showData();
}
I'm not sure if I'm defining the namespace currently.
How Do I call the showData() function from the testNodeMain.cpp file. Currently I'm getting linker error stating that "undefined reference to namespaceName::Node::methodname"
Thanks so much in advance
Okay. That make sense. I removed , using namespace std from header. I'm compiling the testNodeMain.cpp which has the main(). the TestNodeMain.cpp calls functions from testNodeFunctions.cpp. testNodeFunctions.cpp creates Node object.

Answer 1

In your header file node.h, you have
void setData( int x);
int getData();
where as in your node.cpp file, you have:
int Node::getValue() const{
return data;
}
void Node::setValue(int x){
data=x;
}
You need to change your Node::getValue() const {} to Node::getData() const {}, or change the names of the functions in your header files to int getValue() and void setValue (int x)
The function names in the header files for the class and the actual .cpp file should be the same.

Answer 2

It's really hard to tell without a complete compiling example that induces your problem, but it looks like you forgot to include node.cpp on your link line.

Answer 3

I'm not sure if I'm defining the namespace currently.
That looks fine, although without seeing what you've put inside it I can't say for sure.
How Do I call the showData() function from the testNodeMain.cpp file?
The function needs to be declared before you can call it. Add the following declaration, either after the #include lines in testNodeMain.cpp, or in another header file which must then be included from testNodeMain.cpp:
void showData();
Then you can call the function from main:
int main() {
showData();
}
Currently I'm getting linker error stating that "undefined reference to namespaceName::Node::methodname"
You need to make sure you're compiling and linking all the source files, not just the main one. If you're using GCC, the build command should look something like:
gcc -o testNode testNodeMain.cpp testNodeFunctions.cpp node.cpp
If you're still getting the error in that case, then check that you have actually implemented the methods. If you think you have, then please update the code in your question to include the implementation of one of the missing methods so we can check that for you.