FILETIME to ISO format time (string), C++ (vc++)

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//Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23506 for x86

#include <iostream>
#include <windows.h>
#include <string>
#include <sstream>
#include <iomanip>

std::string to_string( FILETIME ftime ) // ISO format, time zone designator Z == zero (UTC)
{
    SYSTEMTIME utc ;
    ::FileTimeToSystemTime( std::addressof(ftime), std::addressof(utc) );

std::ostringstream stm ;
    const auto w2 = std::setw(2) ;
    stm << std::setfill('0') << std::setw(4) << utc.wYear << '-' << w2 << utc.wMonth
        << '-' << w2 << utc.wDay << ' ' << w2 << utc.wYear << ' ' << w2 << utc.wHour
        << ':' << w2 << utc.wMinute << ':' << w2 << utc.wSecond << 'Z' ;

return stm.str() ;
}

int main()
{
    WIN32_FIND_DATA fdata {} ; // {} zero initialise
    const auto handle = ::FindFirstFile( "C:/Windows/system32/ke*.dll", std::addressof(fdata) ) ;

if( handle != INVALID_HANDLE_VALUE )
    {
        do std::cout << std::setw(32) << fdata.cFileName << "    " << to_string(fdata.ftCreationTime) << '\n' ;
        while( ::FindNextFile( handle, std::addressof(fdata) ) ) ;
    }

::FindClose(handle) ;
}

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Compilation time: 2,32 sec, absolute running time: 0,22 sec, absolute service time: 2,55 sec