request for member ' ' in ' ' which is of non_clas... Vtable, Linker error?

Question

When i build my project (gnu g cc, -std=c++11) in Code::BLocks 16.01 on a Win10 x64 Machine, header files are included in the project, i get the following errors:

path..\src\Main.cpp|77|undefined reference to `Snmp_pp::UdpAddress::UdpAddress(char const*)'|

path..\snmp_pp\address.h|574|undefined reference to `vtable for Snmp_pp::UdpAddress'|

And i get a lot of other undefined reference errors.

Here are the parts of my code, there are a lot of commented lines, i skipped them.

main.cpp:

#include <stdio.h>
#include "libsnmp.h"
#include "snmp_pp/snmp_pp.h"
using namespace Snmp_pp;

int main (){
  long rc;
  char buf [256];
  char const* ip_address;
  ip_address = "192.168.127.250";


  Snmp socket_startup();


  //Socket Informationen
   //Here comes line 77***************************
   UdpAddress udp_address(ipaddr);
   snmp_version version = version1;
   int retries = 1;
   int timeout = 100;
   u_short port = 161;
   OctetStr community ("public");

   //SNMP Session öffnen
   int status;

   Snmp snmp(status, 0,(udp_address.get_ip_version()==Address::version_ipv4));
     //SNMP Header Variablen ASN.1 encoding
     Pdu pdu;
     Vb  vb;

      //Erstelle OID Objekte
     Oid oid("1.3.6.1.2.1.1.1.0"); //sysDescr
     vb.set_oid(oid);
     pdu+= vb;
     **Here comes Line 100**
     udp_address.set_port(port);
     **Here comes Line 102**
     CTarget ctarget(udp_address);
     ctartget.set_version(version);
     ctartget.set_retry(retries);
     ctartget.set_timeout(timeout);
     ctartget.set_readcommunity(community);

     SnmpTarget *target;

     target = &ctartget;

     status = snmp.get(pdu, *target);

address.h Here is the UdpAddress Class defined, this is a part of the code

 //------------------------------------------------------------------------
 //---------[ UDP Address Class ]------------------------------------------
 //------------------------------------------------------------------------
 class DLLOPT UdpAddress : public IpAddress
 {
  public:
   /**
    * Construct an empty invalid UDP address.
    */
   UdpAddress();

   /**
    * Construct an UDP address from a string.
    *
    * The following formats can be used additional to those recognized by
    * IpAdress:
    * - Port added to IPv4 address with '/' or ':'
    *   ("192.168.17.1:161", "192.168.17.1/161", "printsrv/161")
    * - Port added to IPv6 address with '/' or using '[...]:'
    *   ("::1/162", "[::1]/162", "[::1]:162")
    *
    * @param inaddr - Hostname or IP address
    */
   UdpAddress(const char *inaddr);

   /**
    * Construct an UDP address from another UDP address.
    *
    * @param udpaddr - address to copy
    */
   UdpAddress(const UdpAddress &udpaddr);

   /**
    * Construct an UDP address from a GenAddress.
    *
    * @param genaddr - address to copy
    */
   UdpAddress(const GenAddress &genaddr);

   /**
    * Construct an UDP address from a IP address.
    * The port will be set to 0.
    *
   * @param ipaddr - address to copy
    */
   UdpAddress(const IpAddress &ipaddr);

 /**
   * Return the IP version of the address.
   *
   * @return one of Address::version_type
    */
   virtual version_type get_ip_version() const { return ip_version; }

   /**
    * Construct an UDP address from a GenAddress.
    *
    * @param genaddr - address to copy
    */
     UdpAddress(const GenAddress &genaddr);

   /**
    * Construct an UDP address from a IP address.
    * The port will be set to 0.
    *
    * @param ipaddr - address to copy
    */
   UdpAddress(const IpAddress &ipaddr);

   /**
    * Destructor (ensure that SnmpSyntax::~SnmpSyntax() is overridden).
    */
   ~UdpAddress() {}

The included header files are from the company HP from the SNMP++3.3.7 project
Link to Page
My folder structure is:

main_dir\src\main.cpp   
main_dir\libsnmp.h   
main_dir\snmp_pp\all other header files  

Heres my build output:

  g++.exe -Wall -std=c++11 -g -std=c++11 -I"C:\Users\Kneringer Georg\Documents\CodeBlocks\SNMP_ZIM" -I"C:\Users\Kneringer Georg\Documents\CodeBlocks\SNMP_ZIM\snmp_pp" -c "C:\Users\Kneringer Georg\Documents\CodeBlocks\SNMP_ZIM\src\Main.cpp" -o obj\Debug\src\Main.o

I need help with understanding what i did wrong. I guess that it is a Linker Error.

Answer 1

In every library (almost), we have two main components:

• Header files containing the declaration of the public functions within the library
• Implementation files where the functions are defined

By including the header files, you tell the compiler, I have these functions at my disposal, you can use them. During the linking phase, the linker will try to find the implementation for these functions, but it doesn't find them that's why you have that error.

In order to fix the error, you need to configure the linker path in your IDE to tell him this is the lib containing the functions.