20 October 2023

File Creation Date and Time

To read the file-time of a file GB32 offers the following functions:

Dim ft As Date
ft = FileDateTime(file$)        // last write time
ft = FileDateTimeAccess(file$)  // last access time
ft = FileDateTimeCreate(file$)  // creation time

They return a Date datatype with resp. the last write time. last access time, and the creation time.

A Date stores a date/time value as an 8-byte real value (Double), representing a date between January 1, 100 and December 31, 9999, inclusive.

The integer part of the Double represents the day:
- The value 2.0 represents January 1, 1900
- 3.0 represents January 2, 1900, and so on.
Adding 1 to the value increments the date by a day.

The fractional part of the value represents the time of day. Therefore, 2.5 represents noon on January 1, 1900; 3.25 represents 6:00 A.M. on January 2, 1900, and so on.
Negative numbers represent dates prior to December 30, 1899.

You can display the Double representation of the current time like this:

Dim dt As Date = Now
Debug CDbl(dt)

The FileDateTime* functions are wrappers around Windows API functions and from their name you expect the date of the last write, last access, or the creation time. For instance, the FileDateTimeCreate() should return the time at which a file is created, thus - for instance - the time a program executed the Open command to create a new file. (BTW the time of the file is not set before the Close command is invoked.) However, if the same file was created earlier, the date/time of the earlier creation is returned!
According to the MS documentation:

"If you rename or delete a file, then restore it shortly thereafter, Windows searches the cache for file information to restore. Cached information includes its short/long name pair and creation time."

Ok, that is a little disappointment, we cannot rely on FileDateTimeCreate to return the file's creation time. What's left is the most obvious function FileDateTime(), which is a kind of default function for a file's time. This first choice function returns the last write time, which seems to be the best thing to get the last time the file was created. The last write time returns the time the file is recreated, last updated or written to. So, you can use FileDateTime to obtain the 'last creation time', because FileDateTimeCreate returns the first creation time. To be sure I tested this by recreating an existing file created first at 3 March 2023:

Open "c:\tmp\test.txt" for Output As # 1
Print # 1; "Text"
Close # 1

After executing these codelines and subsequently choosing the file's properties in the Windows Explorer it indeed still shows a creation date of 3 March 2023. To force the file to a new creation date I changed the code with a Touch command:

Open "c:\tmp\test.txt" for Output As # 1
Print # 1; "Text"
Touch # 1
Close # 1

Now the Windows Explorer properties show the current date as the creation date. Using the Touch command will change all three filedates to the current time. To set each file date separately use one of the SetFileDateTime* functions after closing the file.

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