c++ - Implementing this Abstract Class using a declaration -

i'm implementing automatak opendnp3 libraries c++. want add master channel.as can see definition, parameter action is:

... opendnp3::imasterapplication& appliction, ... 

the imasterapplication interface described here. create masterapplication.cpp , masterapplication.h files , attempt implement class follows:

masterapplication.cpp

 #include "masterapplication.h"   #include <opendnp3/master/imasterapplication.h>   #include <iostream>  #include <chrono>   using namespace opendnp3;  using namespace asiodnp3;  using namespace std;   masterapplication::masterapplication() {     }   masterapplication::~masterapplication() {     } 

masterapplication.h

#ifndef masterapplication_h_ #define masterapplication_h_   #include <opendnp3/master/imasterapplication.h>  #include <opendnp3/link/ilinklistener.h>  #include <openpal/executor/iutctimesource.h>   class masterapplication : public opendnp3::imasterapplication  {  private:   public:     masterapplication();     virtual ~masterapplication();  };   #endif 

but, when try declare masterapplication object in main use:

masterapplication imaster; 

and place within addmaster function, error:

main.cpp:57:20: error: cannot declare variable ‘imaster’ of abstract type ‘masterapplication’    masterapplication imaster; 

what misunderstanding here?

as mentioned in comment, whenever implementing abstract class (interface), pure virtual methods part of abstract class must defined (provided body) in derived class. derived class becomes concrete, , can used type. otherwise becomes abstract.

"so declaration of method make non-abstract?"

not declaration, definition. methods declared (as pure virtual) in base class (interface). giving them definition (body) in derived class makes derived class non-abstract (concrete).

"also, have declare in masterapplication without using it? "

you need define pure virtual methods of base class in derived class. use them or not depend on use-case.