Dependency injection in C++

class builder {
public:
    builder() :
        m_ClassA(NULL),m_ClassB(NULL) {
    }
    ~builder() {
        if (m_ClassB) {
            delete m_ClassB;
        }
        if (m_ClassA) {
            delete m_ClassA;
        }
    }
    ClassA *build() {
        m_ClassB = new class B;
        m_ClassA = new class A(m_ClassB);
        return m_ClassA;
    }
};

ClassA *builder::build(ClassC *classC) {
    m_ClassB = new class B;
    m_ClassA = new class A(m_ClassB, classC);
    return m_ClassA;
}