How can I initialize an array in compile-time with some elements given manually?

If you can change to use std::array then something like this would work.

using func = void (*)();template<int...>struct index_sequence { };template<int From, int N, int... Is>struct make_index_sequence_from : make_index_sequence_from<From, N - 1, N - 1, Is...> { };template<int From, int... Is>struct make_index_sequence_from<From, From, Is...> : index_sequence<Is...> { };template<int... Is> constexprstd::array<func, 256> make_interrupt_vector_array(index_sequence<Is...>){    return {{zero, one, Nth<Is>...}};}constexprstd::array<func, 256> make_interrupt_vector_array(){    return make_interrupt_vector_array(make_index_sequence_from<2, 256>());}constexpr auto interrupt_vector = make_interrupt_vector_array();

I would recommended that you wrap your function around a class/struct so that you can take advantage of template specialization and declare your function as static inside of the class/struct

#include <iostream>template <std::size_t N>struct Nth {    static void print()    {        std::cout << N << "!!" << std::endl;    }};template <>struct Nth<0>{    static void print()    {        std::cout << "Zero!!" << std::endl;    }};template <>struct Nth<1>{    static void print()    {        std::cout << "One!!" << std::endl;    }};int main(){    Nth<0>::print();    Nth<1>::print();    Nth<2>::print();}

Following may help:

#if 1 // Not in C++11#include <cstdint>template <std::size_t ...> struct index_sequence {};template <std::size_t N, std::size_t ...Is>struct make_index_sequence : make_index_sequence <N - 1, N - 1, Is...> {};template <std::size_t ... Is>struct make_index_sequence<0, Is...> : index_sequence<Is...> {};#endif // make_index_sequenceusing func = void (*)();namespace detail{// general casetemplate <std::size_t N>struct FuncPtr { static constexpr func value = &Nth<N>; };// Some specializations // not necessary at the beginningtemplate <>struct FuncPtr<0u> { static constexpr func value = &zero; };template <>struct FuncPtr<1u> { static constexpr func value = &one; };// Function to create the array:template <std::size_t ... Is>constexpr std::array<func, sizeof...(Is)>FuncPtrArray(index_sequence<Is...>){    return std::array<func, sizeof...(Is)>{{FuncPtr<Is>::value...}};}} // namespace detailconstexpr std::array<func, 256> interrupt_vector =    detail::FuncPtrArray(make_index_sequence<256>());