How can I detect file change?!

[alexiworld]

Hi everybody,

I want to develop module that detects file's change. I mean than your application will be notified through that module when somebody changes file outside. I found some convinient ways to do this job in Win32. I'm using FindFirstChangeNotification, FindNextChangeNotification and ReadDirectoryChangesW functions. But after using them I must look for changed file because these function doesn't give me information about which one is the changed file. Does anybody knows how to do this task? The simplest way is to check date of modification of file. But I wonder myself whether there is any more direct way.

Also does anybody knows how to do this detection on Unix/Linux?!

Regards, Alex

[alexiworld]

I saw that ReadDirectoryChangesW function returns FILE_NOTIFY_INFORMATION structure but this function is not supported on Windows 9x according to the MSDN. This makes me to use FindFirstChangeNotification, FindNextChangeNotification functions on Windows 9x. So anybody who has some advise for the last is welcome.

Regards, Alex

[filthy_mcnasty]

well to see if there has been a change to a file you can run it against a CRC32 value you know to represent the file prior to modification.

to actually FIND each change in the file though would be lots harder and i'm not familiar with how to do that. there are programs around though *some ship w/ windows* that do things like that and you could take those and view their import tables to get an idea of how it's doing it (that's a very handy way to get a GENERAL idea)

search the forum for CRC and you'll find a ton of stuff

[alexiworld]

I'm not looking for the change inside the file. There are a lot of tool that do this job very pretty (like diff).
I'm looking for notification which file was changed outside my aplication. I have some ideas about FindFirstChangeNotification&FindNextChangeNotification. I can wait on event handle for each one of directories that I want to observe with WaitForSingleObjectEx function. In this way I can detect exact directory in which change occured. If somebody has better idea let me know.


Regards, Alex

PS: What about Unix/Linux?! I'll be very surprised if these OS doesn't support such kind of feature like this one supported in Windows.

[avantos]

I only know of how to do this in unix, and in C. I don't think there is anything in C++, but you could easily make a class from this.

You are looking for the library <sys/stat.h>.

Function: int stat(char *path, struct stat *buf).

what struct stat is: (i put comments by what you will need)

struct stat {
mode_t st_mode;
ino_t st_ino;
dev_t st_dev;
dev_t st_rdev;
nlink_t st_nlink;
uid_t st_uid;
gid_t st_gid;
off_t st_size; // file size
time_t st_atime; // time file was last accessed
time_t st_mtime; // time of last modification
time_t st_ctime; // time of last file status change...
// this one is like ctime in that it is in seconds from
// jan 1, 1970...
long st_blksize;
blkcnt_t st_blocks;
}

This is just very basic, you'll probably need to look up more on the net, but this should point you in the right direction. One thing your obviously going to have to do is save all the data somewhere, save the last size, last changed time, etc. Then when you check again, see if it changed.

-Avantos

[DanM]

1) stat (in fact _stat) is also available in Windows but it is just a wrapper around other OS primitives:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore98/html/_crt__stat.2c_._wstat.2c_._stati64.2c_._wstati64.asp


2) You can try fcntl with F_NOTIFY (on Linux at least):

File and directory change notification
F_NOTIFY
(Linux 2.4 onwards) Provide notification when the directory referred to by fd or any of the files that it contains is changed. The events to be notified are specified in arg, which is a bit mask specified by ORing together zero or more of the following bits:
Bit Description (event in directory)

DN_ACCESS
DN_MODIFY A file was modified (write, pwrite,

writev, truncate, ftruncate)

DN_CREATE A file was created (open, creat, mknod,

mkdir, link, symlink, rename)

DN_DELETE A file was unlinked (unlink, rename to

another directory, rmdir)

DN_RENAME A file was renamed within this

directory (rename)

DN_ATTRIB The attributes of a file were changed

(chown, chmod, utime[s])

Here is a link to the fcntl man pages:
http://www.item.ntnu.no/cgi-bin/man2html?fcntl+2

Dan

[alexiworld]

Thank you Dan,
Yesterday I found such as article in Internet - http://nst.dsi.a-star.edu.sg/mcsa/lxr/linux/source/Documentation/dnotify.txt

The idea is the same with yours. I test it on linux core 2.4.19 onward and it works. But for my sorrow I didn't find something similar on Unix (Solaris). Some gues told me that there isn't such as. This makes me to think that Win is better. But this is another theme which place is not here.

Regards, Alex