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hello-world.cpp

class I_A {
public:
    virtual void func1() = 0;
};

class C_A : public I_A {
public:
    C_A() { }

    void func1() override { }
};

class I2_A : public I_A {
public:
    virtual void func2() = 0;
};

class C2_A : public I2_A, public C_A {
public:
    C2_A() : C_A() { }

    void func2() override { }
};

int main(int argc, char *argv[])
{
    C2_A a2;
    a2.func1();
    a2.func2();

    return 0;
}