#include <cstdint>
#include <vector>
#include <cstring>
#include <fstream>
#include <bit>

struct Header_t {
    uint32_t field1;
    uint16_t field2;
    uint16_t field3;
};

int main() {
    std::ifstream file("abu.bin", std::ios::in | std::ios::binary);
    std::streampos fileSize = 0x12345;
    std::vector<uint8_t> buf(fileSize);
    uint8_t* pBuf = buf.data();
    file.read(reinterpret_cast<char*>(pBuf), fileSize); // (1)
    Header_t header;
    header = *reinterpret_cast<Header_t*>(pBuf);  // (2)
    //              ^ v одно и тоже
    header = *static_cast<Header_t*>(static_cast<void*>(pBuf)); // (3)
    std::memcpy(&header, pBuf, sizeof(Header_t));             // (4)
    header = *std::bit_cast<Header_t*>(pBuf);               // (5)
    static_assert(std::is_trivial_v<Header_t> &&
         std::is_standard_layout_v<Header_t>);
    return 0;
}