Question

I have a class Child and a class Human where Human has all the functions declared in Child as virtual functions. And a class Child inherits from Human class.

I want to use Human as a interface file to hide implementation in Child.

I didn’t really set up a constructor, but I set up an init() function which initializes basic settings.

Now, what is a good way that I can use Child functions using Human interface file?

I tried

Human *John = new Child();

but I got the following errors.

main.cpp:7: error: expected type-specifier before ‘Child’
main.cpp:7: error: cannot convert ‘int*’ to ‘Human*’ in initialization
main.cpp:7: error: expected ‘,’ or ‘;’ before ‘Child

I don’t understand where int* came from either. None of my functions declared returns int*.

edit

main.cpp

#include <stdlib.h>
#include <stdio.h>
#include "Human.h"
using namespace std;
int main(){

    Human *John = new Child();

    return 0;
}

human.h

#ifndef __HUMAN_h__
#define __HUMAN_h__


class Human
{
public:
    virtual void Init() = 0;
    virtual void Cleanup() = 0;
};


#endif

Child.h

#ifndef __CHILD_h__
#define __CHILD_h__

#include "Human.h"


class Child : public Human
{
public:
    void Init();
    void Cleanup();

};

#endif

Child.cpp

#include "Child.h"
void Child::Init()
{
}

void Child::Cleanup()
{
}

Makefile

CC = g++
INC = -I.
FLAGS = -W -Wall
LINKOPTS = -g

all: program

program: main.o Child.o
    $(CC) -Wall -o program main.o Child.o

main.o: main.cpp Human.h
    $(CC) -Wall -c main.cpp Human.h

Child.o: Child.cpp Child.h
    $(CC) -Wall -c Child.cpp Child.h

Child.h: Human.h

clean:
    rm -rf program

Answer 1

You need to #include "Child.h" in your cpp file. You can do this along with including human.h or you can not include human.h as that will be brought in automatically by the include within child.h

#include <stdlib.h>
#include <stdio.h>
#include "Child.h"
#include "Human.h"    // This is no longer necessary, as child.h includes it  
using namespace std;
int main(){
    Human *John = new Child();
    return 0;
}