File Times - Win32 Programmer's Reference

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File Times

A file time represents the specific date and time at which a given file was created, last accessed, or last written to. Windows records file times whenever applications create, access, and write to files. Windows records the times using a 64-bit value specifying the number of 100-nanosecond intervals that have elapsed since 12:00 A.M. January 1, 1601 (UTC). Writing to a file changes the last write time; writing to or reading from the file (including running an executable file) changes the last access time.

Note Not all file systems can record creation and last access time. In particular, the file allocation table (FAT) file system records only last-write times.

You can retrieve the file times for a given file by using the GetFileTime function. GetFileTime copies the creation, last access, and last write times to individual FILETIME structures. Each structure consists of two 32-bit values that combine to form the single 64-bit value. You can also retrieve the file times by using the FindFirstFile and FindNextFile functions. These functions copy the times to FILETIME structures in a WIN32_FIND_DATA structure.

You can set the file times for a file by using the SetFileTime function. This function lets you modify creation, last access, and last write times without changing the content of the file. You can compare the times of different files by using the CompareFileTime function. The function compares two file times and returns a value indicating which time is greater or returns zero if the times are equal.

To make a file time more meaningful to a user, you can extract the month, day, year, and time of day from a file time by using the FileTimeToSystemTime function. FileTimeToSystemTime converts the file time and copies the individual values for date and time of day to a SYSTEMTIME structure.

Windows records all file times in UTC-based times, but you can convert a file time to the local time for your time zone by using the FileTimeToLocalFileTime function. Before displaying a file time to a user, applications typically convert the file time to local time, then extract the month, day, year and time of day using FileTimeToSystemTime.

If you plan to modify file times for given files, you can convert a date and time of day to a file time by using the SystemTimeToFileTime function. You can also obtain the system time FILETIME structure by calling the GetSystemTimeAsFileTime function.

If the original date and time of day are given in the local time for your time zone, you can convert the resulting file time to UTC by using the LocalFileTimeToFileTime function. Always make sure the file times you set using SetFileTime are valid UTC-based times.

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