Method const_buffer

3rdparty/cppzmq/zmq.hpp:1125–1125

{
  public:
    constexpr const_buffer() noexcept : _data(nullptr), _size(0) {}
    constexpr const_buffer(const void *p, size_t n) noexcept : _data(p), _size(n)
    {
#ifdef ZMQ_EXTENDED_CONSTEXPR