CODEWITHSUNDEEP
c++winapifilesystems
Recker
Recker

Reputation: 1975

Unreadable file attributes on windows

Consider a following snippet of code

    #include <iostream>
    #include <windows.h>
    int main()
    {
        WIN32_FILE_ATTRIBUTE_DATA  wfad;

        GetFileAttributesEx(("C:\\TEMP\\noreadfile"), GetFileExInfoStandard, &wfad); //"noreadfile" is unreadable file
        std::cout << wfad.dwFileAttributes;  // 128                                                 
        return 0;
    }

For an unreadable file (File that does not have read permissions or file that has its read permissions set as "Deny" in its properties -> security tab) on Windows, GetFileAttributesEx returns FILE_ATTRIBUTE_NORMAL, which means that no other attribute is set for that file.

This attribute is also returned for a writeable as well as non-readonly files.

We use this information to set the permissions for files in our product code.

We concluded that GetFileAttributesEx might be returning incorrect attribute in case of unreadable files. We wonder if our conclusion is right or not.

If yes, then is this a known issue with GetFileAttributesEx ?

If not then

What is the correct way to get the file attributes (file permissions perhaps ?) for an unreadable file using Windows API or if possible using Boost or standard C++ filesystem libraries ?

Upvotes: 0

Views: 479

Answers (1)

David A
David A

Reputation: 394

It's probably not succeeding at all. If you look at the documentation for GetFileAttributesEx, it actually returns a BOOL.

Return value If the function succeeds, the return value is a nonzero value.

If the function fails, the return value is zero (0). To get extended error information, call GetLastError.

My guess is that "fwad" is undefined if the call fails. Try checking the return value for a failure indication. My guess is that GetLastError will return something like ERROR_ACCESS_DENIED.

The Windows API doesn't throw exceptions, so unfortunately you'll have to check just about every return value.

Upvotes: 1

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