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.NET Forum / Languages / Managed C++ / November 2007Parameters to CreateFile
What arguments do I need to give CreateFile? I want to open a file or folder for reading, even if it is already opened from another place. I'm trying: CreateFile (argv[1], GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL) but this fails to open folders ("Access is Denied") or files that are already used (as far as I understand). >What arguments do I need to give CreateFile? I want to open a file or folder >for reading, even if it is already opened from another place. You can only do that if the "other place" has also allowed sharing. I have a simple test application for the CreateFile API that I use for checking such scenarios: http://www.jddesign.f2s.com/freeware_programs.htm#CFTest Dave Thanks. The test opens successfully the file that is supposed to be used already, and fails to open any directory that I try it on claiming 5: "Access is denied". What does that mean? > I have a simple test application for the CreateFile API that I use for > checking such scenarios: > http://www.jddesign.f2s.com/freeware_programs.htm#CFTest > > Dave >Thanks. The test opens successfully the file that is supposed to be used >already, and fails to open any directory that I try it on claiming 5: "Access >is denied". What does that mean? You have to specify FILE_FLAG_BACKUP_SEMANTICS to open a directory, the test doesn't do that. Dave Indeed. It goes in the parameter before last in CreateFile. (However, the "used" file is still opened by the test but not by my function call.) > You have to specify FILE_FLAG_BACKUP_SEMANTICS to open a directory, > the test doesn't do that. > > Dave >Indeed. It goes in the parameter before last in CreateFile. >(However, the "used" file is still opened by the test but not by my function >call.) I don't understand what you're telling me there. My test program doesn't use the FILE_FLAG_BACKUP_SEMANTICS option, so it's not useful for testing opening directories. Dave I have a file that the test opens successfully, but my CreateFile syscall fails on it claiming that it's opened by another process. The other process is Visual Studio and the file is <project>.ncb . > I don't understand what you're telling me there. >I have a file that the test opens successfully, but my CreateFile syscall >fails on it claiming that it's opened by another process. So what options are you using differently? >The other process is Visual Studio and the file is <project>.ncb . What are you trying to do? I would expect VS to open the NCB file exclusively - it's not the sort of thing that it'd want to be opened by another process. Dave > >I have a file that the test opens successfully, but my CreateFile syscall > >fails on it claiming that it's opened by another process. > > So what options are you using differently? None. The same call, except that I added FILE_FLAG_BACKUP_SEMANTICS . > >The other process is Visual Studio and the file is <project>.ncb . > > What are you trying to do? Check the size of the file > I would expect VS to open the NCB file exclusively - it's not the sort > of thing that it'd want to be opened by another process. So I guess that this solves the problem: What I'm trying to do can't be done with opening the file. I found that it can probably be done with GetFileAttributesEx - see http://blog.kowalczyk.info/kb/get-file-size-under-windows.html . >> >The other process is Visual Studio and the file is <project>.ncb . >> >> What are you trying to do? >Check the size of the file No need to open it then, just use FindFirstFile, FindClose. Dave Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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