CODEWITHSUNDEEP
c++cwindows
Javier Mr
Javier Mr

Reputation: 2200

How to detect if file is openned by other process in windows

I'm opening files using the _findfirst function in windows, but I will only want to open files which are not opened by other process. The situation is that I will scan a directory read the files and delete them while other process create new files in it.

To avoid race conditions I found this question which mentions the possibility to open a file with a no sharing option. But how is that done?

Update: I have no control about the writing process, so don't know which flags, if nay, are used when creating a file. Moreover the writing process may change (third party software).

Upvotes: 2

Views: 1988

Answers (3)

João Amaral
João Amaral

Reputation: 331

Assuming that your 2 processes are the only ones that will open the files then, from MSDN open sample:

hFile = CreateFile(argv[1],                // name of the write
                       GENERIC_WRITE,          // open for writing
                       0,                      // *** do not share ***
                       NULL,                   // default security
                       CREATE_NEW,             // create new file only
                       FILE_ATTRIBUTE_NORMAL,  // normal file
                       NULL);                  // no attr. template

By using this in your writing process you can then check for INVALID_HANDLE_VALUE in the reading process and in this case if GetLastError() returns ERROR_SHARING_VIOLATION then you know that your file is opened by another process with no sharing.

More details can be found in the CreateFile documentation

Upvotes: 3

aneesh jose
aneesh jose

Reputation: 381

to open a file with no sharing option, you can use

HANDLE hFile = CreateFile("somFileName",
                      GENERIC_WRITE,
                      0, /*no sharing; other options are FILE_SHARE_READ, FILE_SHARE_WRITE etc*/
                      NULL,
                      OPEN_EXISTING,
                      FILE_ATTRIBUTE_NORMAL,
                      NULL);

Upvotes: 1

Hatted Rooster
Hatted Rooster

Reputation: 36483

Call OpenFile and as uStyle (third param) add at least OF_SHARE_EXCLUSIVE.

Upvotes: 1

Related Questions