#include <iostream>
#include <math.h>
#include <string.h>

using namespace std;

class Foo {
protected:
    char *foo;

public:
    Foo() {
        foo = NULL;
    }
    Foo(char *str) {
        foo = new char[100];
        strcpy(foo, (str) ? str : "");
    }
    virtual ~Foo() {
        if (foo) {
            delete [] foo;
        }
    }

    void* data() {
        return foo;
    }
    int display() {
        cout << foo << endl;
    }
};

class Bar: public Foo {
public:
    Bar(char c) {
        foo = new char;
        *foo = c;
    }
    ~Bar();
};

int main(void) {
    Foo one("this is a foo ");
    Bar two('F');
    one.display();
    two.display();

    return 0;
}



bhearsum@gaz:~/tmp$ gcc -lstdc++ -o test test.cpp
/tmp/ccZ3rM8T.o: In function `main':test.cpp:(.text+0x67): undefined reference to `Bar::~Bar()'
:test.cpp:(.text+0x7a): undefined reference to `Bar::~Bar()'
/tmp/ccZ3rM8T.o: In function `Bar::Bar(char)':test.cpp:(.gnu.linkonce.t._ZN3BarC1Ec[Bar::Bar(char)]+0x19): undefined reference to `vtable for Bar'
collect2: ld returned 1 exit status