Using qsort with lambdas

qsort.inl

template <typename T>
struct Compare {
    T lambda;

#if _MSC_VER || __APPLE__
    static int compare(void * cmp, const void * a, const void * b)
#else
    static int compare(const void * a, const void * b, void * cmp)
#endif
    {
        return ((Compare<T>*)cmp)->lambda(a, b);
    }
};

template <typename F>
void qsort(void *base, size_t num, size_t width, F cmp) {
    Compare<F> f { cmp };
#if _MSC_VER
    qsort_s(base, num, width, Compare<F>::compare, &f);
#elif __APPLE__
    qsort_r(base, num, width, &f, Compare<F>::compare);
#else
    qsort_r(base, num, width, Compare<F>::compare, &f);
#endif
}