_open generate "Access is denied" error

_Flaviu

Confidence that I have solved all strange errors here, I come back with some issue generated by a legacy C code for linux, code that I intend to use it in a MFC app in windows OS. Ok. I have a simple code:

int nRespond = _open(device, 020);
UINT err = ::GetLastError();

where devide is const char* and has value C (or D:, or E: ) The nRespond is -1 and err has value 5, which is mean Access is denied. What could be the problem here ? I ran the test app as administrator mode (ran from VS2017 as admin mode).

Graham Breach

The problem appears to be that you are expecting Linux code to work on Windows. The _open function opens a file - on unix systems you can open directories and devices as files, but not on Windows. If you're lucky the code is actually expecting a normal file and you just passed in a device letter by mistake. Otherwise you will have to port the code, replacing the Linux system functions with code that does the same thing on Windows.

Lost User

You cannot access raw devices on Windows by their drive letters, you must use their volume identifiers. See File path formats on Windows systems | Microsoft Docs[^].

leon de boer

Your flags (020) are linux flags not windows try ( _O_WRONLY | _O_CREAT ) or some normal windows flags _open, _wopen | Microsoft Docs[^] I would add even in linux the code really should be written as flags not a value like that for this exact reason.

In vino veritas

_Flaviu

I have tried this:

int nRespond = _open(device, _O_WRONLY | _O_CREAT);
UINT e = ::GetLastError();

with the same result (error 5). Strange ....

_Flaviu

So I cannot open disk with this function ? ... this is the original code ... strange ...

_Flaviu

I also tried this:

#include int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{

\_open("D:", 0x02 | 0x04);
UINT e = ::GetLastError();
cout << e;

}

from cmd line as administrator rights … the same result: 5 (access is denied).

Lost User

_Flaviu wrote:

this is the original code

From where?

leon de boer

Big Errors You can't open "D:" that isn't a file ... its not linux you don't mount drives Try

int nRespond = _open("D:\\somefilename.txt", _O_WRONLY | _O_CREAT);
UINT e = ::GetLastError();

I am sure it will open :-)

In vino veritas

_Flaviu

Agree. Is there any windows methods to open a disk and get the handle ? Because this nResponse it is used further as a handle ...

_Flaviu

I get this code from a plain C code which has built for Linux:

int nRespond = _open(device, 020);

Lost User

You cannot run Linux code on Windows without adjusting it for the differences. Windows does not let you address raw devices in the same way that Linux does. And in fact doing so is very dangerous as you could destroy your entire system.

_Flaviu

And is any other method to open a device rather than _open in Windows ? I think I have to made some changes into Linux code to run on Windows ...

Lost User

I gave you a link in my first message above which shows details of how to address devices in Windows. However, the real question is, what exactly are you trying to do?

Victor Nijegorodov

Yes. It is [CreateFile function (fileapi.h) | Microsoft Docs](https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea)

_Flaviu

Good idea. I have used CreateFileA, and I get rid of that "access denied". But there a thing that I had afraid: the original code, with _open returned int, and CreateFileA return HANDLE ... casting HANDLE to int is OK ? I guess not ...

Victor Nijegorodov

How are you going to use the handle returned from _open ?

leon de boer

Windows has GetLastError you notice CreateFile Simply returns invalid handle for an error if you get that then you call GetLastError GetLastError function (errhandlingapi.h) | Microsoft Docs[^] That is the equivalent of your original int it's just a non zero number identifying the error, 0 always equals no error.

In vino veritas