FILETIME to __int64

Question

What is the proper way to convert a FILETIME structure into __int64? Can you please tell me?

Answer 1

I don't think you're suppose to: "Do not cast a pointer to a FILETIME structure to either a ULARGE_INTEGER* or __int64* value because it can cause alignment faults on 64-bit Windows."

Source.

If you really wanted it would be something like:

__int64 to_int64(FILETIME ft)
{
    return static_cast<__int64>(ft.dwHighDateTime) << 32 | ft.dwLowDateTime;
}

FILETIME ft = // ...
__int64 t = to_int64(ft);

But something like:

FILETIME ft = // ...
__int64 t = *reinterpet_cast<__int64*>(&ft);

Is bad.

Answer 2

There is no need to revert to arcane constructs using bitwise OR's. The Windows API has got everything you need to do this.

unsigned __int64    convert( const FILETIME & ac_FileTime )
{
  ULARGE_INTEGER    lv_Large ;

  lv_Large.LowPart  = ac_FileTime.dwLowDateTime   ;
  lv_Large.HighPart = ac_FileTime.dwHighDateTime  ;

  return lv_Large.QuadPart ;
}  

Or if you want to go to __int64 directly.

__int64 convert_to_int64( const FILETIME & ac_FileTime )
{
  return static_cast< __int64 > ( convert( ac_FileTime ) ) ;
}

Answer 3

Try

(__int64(filetime.dwHighDateTime)<<32) | __int64(filetime.dwLowDateTime)

Answer 4

Of course you could just pass in an __int64 casted to a filetime as follows *(FILETIME*)&int64Val. This will work fine under Visual C++.

ie

__int64 createTime = 0;
__int64 accessTime = 0;
__int64 writeTime = 0;
GetFileTime( hFile, *(FILETIME*)&createTime, *(FILETIME*)&accessTime, *(FILETIME*)&writeTime );

Answer 5

you can try the code follow. the code is from chromium project

template <class Dest, class Source>
inline Dest bit_cast(const Source& source) {
    Dest dest;
    memcpy(&dest, &source, sizeof(dest));
    return dest;
}

//FILETIME to __int64

__int64 FileTimeToMicroseconds(const FILETIME& ft) {
    return bit_cast<__int64, FILETIME>(ft) / 10;
}

void MicrosecondsToFileTime(__int64 us, FILETIME* ft) {
    *ft = bit_cast<FILETIME, __int64>(us * 10);
}

int _tmain(int argc, _TCHAR* argv[])
{
    __int64 nTmpUint64 = 13060762249644841;

    time_t unixtime;
    FILETIME nTmpFileTm;
    MicrosecondsToFileTime(nTmpUint64,&nTmpFileTm);

    return 0;
}

Answer 6

I had exactly the same issue, googled for it, and came here. But I also found a useful Microsoft support page at
https://support.microsoft.com/en-gb/help/188768/info-working-with-the-filetime-structure

It says:

---

Performing Arithmetic with File Times

It is often necessary to perform a simple arithmetic on file times. For example, you might need to know when a file is 30 days old. To perform an arithmetic on a file time, you need to convert the FILETIME to a quadword (a 64-bit integer), perform the arithmetic, and then convert the result back to a FILETIME.

Assuming ft is a FILETIME structure containing the creation time of a file, the following sample code adds 30 days to the time:

   ULONGLONG qwResult;

   // Copy the time into a quadword.
   qwResult = (((ULONGLONG) ft.dwHighDateTime) << 32) + ft.dwLowDateTime;

   // Add 30 days.
   qwResult += 30 * _DAY;

   // Copy the result back into the FILETIME structure.
   ft.dwLowDateTime  = (DWORD) (qwResult & 0xFFFFFFFF );
   ft.dwHighDateTime = (DWORD) (qwResult >> 32 );

---

Edit: I realise this merely confirms some of the other answers, but I thought it was worth adding for clarification.

Answer 7

Three ways that have best performance (one assembler instruction). Tested only in Visual C++ 2022 x64.

auto u = std::bit_cast<std::uint64_t>(ft)

The best way.

auto u = *reinterpret_cast<std::uint64_t _UNALIGNED*>(&ft)

Disadvantage: _UNALIGNED macro (and __unaligned modifier) is non-standard. But almost every compiler has this modifier in some form.

memcpy(&u, &ft, sizeof(u))

Disadvantage: this code will be well optimized only if you turn on “Enable Intrinsic Functions” C++ compiler option.

Other answers have some overheads.

(static_cast<std::uint64_t>(ft.dwHighDateTime) << 32) | ft.dwLowDateTime

Generates bitwise operations.

ULARGE_INTEGER{ft.dwLowDateTime, ft.dwHighDateTime}.QuadPart

Generates two 32-bit operations instead of one 64-bit one.