Which WinAPI function checks permissions of a specific file/folder? [duplicate] - winapi

Question

In win32 c++; is there a way to determine if a folder/file is accessible? You know how if you try to access a certain folder in the C:/Windows directory & you will get a popup saying "This folder is not accessible".
Maybe there is a file attribute constant that signifies that the file is private? Maybe something like FILE_ATTRIBUTE_PRIVATE?
WIN32_FIND_DATA dirData;
while (FindNextFile( dir, &dirData ) != 0 )
{
// I made the following constant up
if ( !(fileData.dwFileAttributes & FILE_ATTRIBUTE_PRIVATE) )
{
// file is accessible so store filepath
files.push_back( fileData.cFileName );
}
else // file is not accessible so dont store
}
Or is the only way to know by going:
dir = FindFirstFileEx( (LPCTSTR)directory.c_str(), FindExInfoStandard, &dirData, FindExSearchNameMatch, NULL, 0 );
if ( dir == ??? ) { the file is inaccessible } [/code]

Answer 1

Best thing to do is just try to access it.
You can calculate the access granted by the access control list for a particular user account, but this is quite complicated, and the permission could change after you do the access check. So just open the file and handle access denied errors.

Answer 2

It wouldn't be a flag on the file itself because different accounts may have access to different files/directories. Instead, windows uses ACL's (access control lists), which are data structures that determine who has access to what.
ACLs in windows can be used with just about anything that is referred to by a handle (files, directories, processes, mutexes, named pipes...). You can view file ACLs by going to properties of a file and view "Security" tab.
So in your app you don't really want to check for a flag, but to compare file's ACL against the user account under which your app is running. Check out AccessCheck Win32 function. I think it's exactly what you are looking for.
Personally, I've never used that function, but if you are looking for Win32 solution and you want a function call, that's probably your best bet. However, as others have pointed out, it might be too complicated. I've always used _access (or _waccess) which is part of CRT, uber easy to use, and you don't take a performance hit of acquiring a file handle only to close it (depending on how tight your loop is, those calls can actually add up).

Answer 3

int _access(
const char *path,
int mode
);
Simple to use:
http://msdn.microsoft.com/en-us/library/1w06ktdy%28v=vs.80%29.aspx

Answer 4

Yes Aaron Ballman you are a boss! Oh man oh man! Which I could use some useful expletives to expressives my joy right now.
https://blog.aaronballman.com/2011/08/how-to-check-access-rights/ is a link to the example of checking accesss rights in win32 on a fpath. And the explanation behind the poorly documented AccessCheck win32 function. Below is the code.
bool canAccessPath( LPCTSTR folderName, DWORD genericAccessRights )
{
bool bRet = 0;
DWORD length = 0;
if (!::GetFileSecurity( folderName, OWNER_SECURITY_INFORMATION|GROUP_SECURITY_INFORMATION|DACL_SECURITY_INFORMATION, NULL, 0, &length ) &&
ERROR_INSUFFICIENT_BUFFER == ::GetLastError())
{
PSECURITY_DESCRIPTOR security = static_cast< PSECURITY_DESCRIPTOR >( ::malloc( length ) );
if (security && ::GetFileSecurity( folderName, OWNER_SECURITY_INFORMATION|GROUP_SECURITY_INFORMATION|DACL_SECURITY_INFORMATION, security, length, &length ))
{
HANDLE hToken = NULL;
if (::OpenProcessToken( ::GetCurrentProcess(), TOKEN_IMPERSONATE|TOKEN_QUERY|TOKEN_DUPLICATE|STANDARD_RIGHTS_READ, &hToken ))
{
HANDLE hImpersonatedToken = NULL;
if (::DuplicateToken( hToken, SecurityImpersonation, &hImpersonatedToken ))
{
GENERIC_MAPPING mapping = { 0xFFFFFFFF };
PRIVILEGE_SET privileges = { 0 };
DWORD grantedAccess = 0, privilegesLength = sizeof( privileges );
BOOL result = FALSE;
mapping.GenericRead = FILE_GENERIC_READ;
mapping.GenericWrite = FILE_GENERIC_WRITE;
mapping.GenericExecute = FILE_GENERIC_EXECUTE;
mapping.GenericAll = FILE_ALL_ACCESS;
::MapGenericMask( &genericAccessRights, &mapping );
if (::AccessCheck( security, hImpersonatedToken, genericAccessRights,
&mapping, &privileges, &privilegesLength, &grantedAccess, &result ))
{
bRet = result == TRUE;
}
::CloseHandle( hImpersonatedToken );
}
::CloseHandle( hToken );
}
::free( security );
}
}
return bRet;
}
Don't be shy to pop into his website and check out his work. I am sure he has more interesting stuff.