CODEWITHSUNDEEP
c++
k4iru
k4iru

Reputation: 33

C++ undefined namespace

I'm trying to create a header file, implementation file and main file for a simple c++ program that returns the systems hostname using gethostname().

my header file that declares my class, data, and methods

//hostname.h
#pragma once                                                                                              

namespace hostnamespace
{
  class hostname_class
  {
    public:
      hostname_class();
      void to_string();

    private:
      char *name;
  };  
}

my implementation file that defines my class and methods

//hostname_class.cpp
#include "hostname.h"                                                                                     
#include <iostream>
#include <unistd.h>
#include <limits.h>

using namespace hostnamespace;
using namespace std;

class hostname_class{
  private:
    char *name;
  public:
    hostname_class(){
      gethostname(name, HOST_NAME_MAX);
    }   
    void to_string(){
      cout << "Hostname:" << &name << endl;
    }   
};

my main program file

//hostname_main.cpp
#include "hostname.h"                                                                                     
#include <iostream>

using namespace hostnamespace;

int main() {
  hostname_class host;
  host.to_string();
  return 0;
}

when I try and run g++ -o main hostname_main.cpp hostname_class.cpp

I get this error 

/bin/ld: /tmp/ccGfbyuu.o: in function `main':
hostname_main.cpp:(.text+0x1f): undefined reference to `hostnamespace::hostname_class::hostname_class()'
/bin/ld: hostname_main.cpp:(.text+0x2b): undefined reference to `hostnamespace::hostname_class::to_string()'
collect2: error: ld returned 1 exit status

any help would be appreciated.

Upvotes: 0

Views: 1304

Answers (1)

selbie
selbie

Reputation: 104474

You are redeclaring the hostname_class in the global namespace instead of defining it within the namespace you intended.

A sample structure of how your hostname_class.cpp file could be written.

#include <iostream>
#include <unistd.h>
#include <limits.h>
#include "hostname.h"

using namespace std;

namespace hostnamespace
{

    hostname_class::hostname_class() {
        gethostname(name, HOST_NAME_MAX);
    }   

    void hostname_class::to_string() {
      cout << "Hostname:" << name << endl;
    }   
};

One side note - I literally copied your method implementations verbatim. It will compile. But name is certainly uninitialized and pointing to an undefined memory address when you pass it into gethostname. That's probably not good.

Upvotes: 4

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