The Byte Order Fiasco(justine.lol)

    u32::from_le_byte(bytes) // u32 from 4 bytes, little endian
    u32::from_be_byte(bytes) // u32 from 4 bytes, big endian
    u32::to_le_bytes(num) // u32 to 4 bytes, little endian
    u32::to_be_bytes(num) // u32 to 4 bytes, big endian

    #include <boost/endian.hpp>
    #include <cstdio>
    using namespace boost::endian;

    unsigned char b[5] = {0x80,0x01,0x02,0x03,0x04};

    int main() {
        uint32_t x = *((big_uint32_t*)(b+1));
        printf("%08x\n", x);
    }

    static inline uint32_t read32be(const uint8_t *p)
    {
        return (uint32_t)p[0] << 24
             | (uint32_t)p[1] << 16
             | (uint32_t)p[2] <<  8
             | (uint32_t)p[3];
    }

    The  "Be reasonable, do it my way" approach does not work.  Neither does the Esperanto approach of "let's all switch to yet a new language".

    It is more important to  agree  upon an order than which order is agreed upon.

  static uint32_t load32_le(const uint8_t s[4])
  {
      return (uint32_t)s[0]
          | ((uint32_t)s[1] <<  8)
          | ((uint32_t)s[2] << 16)
          | ((uint32_t)s[3] << 24);
  }

    (uint32_t)x[0] << 24 | ...

    if constexpr (std::endian::native == std::endian::big) {
        std::cout << "big-endian" << '\n';
    }
    else if constexpr (std::endian::native == std::endian::little) {
        std::cout << "little-endian"  << '\n';
    }
    else {
        std::cout << "mixed-endian"  << '\n';
    }