Thread: C Delete opened file

Hi,

I am in the early stages of learning C (previously coded in java, PHP etc.).

The code below is a simple menu which enables you to:
create, delete, open and close a file.

The problem i have is if you choose to create the file, then open it, it is then not possible to delete it (gives error 32).
If you delete without opening it works fine or if you restart the program and then delete the file that was created in the last run it is also ok. Just seems you cant create, open and delete in same operation.

Any input would be helpful.

Code:

// for Win Xp Pro
#define _WIN32_WINNT 0x0501
#include <windows.h>
#include <stdio.h>

int main()
{
  HANDLE hFile;
  char fname[30] = "C:\\testfile.txt";
  int menuOption;

do {
      printf("\n");
      printf("0) Exit\n");
      printf("1) Close File\n");
      printf("2) Delete File\n");
      printf("3) Create File\n");
      printf("4) Open File\n");
      scanf("%d", &menuOption);

    switch(menuOption)
    {
        case 0 :
            break;
        case 1 :
            //close option
            if(CloseHandle(hFile) != 0)
              printf("CloseHandle() succeeded!\n");
            else printf("CloseHandle() failed!\n");
            break;
        case 2 :
            //delete option
            if(CloseHandle(hFile) != 0)
              printf("CloseHandle() succeeded!\n");
            else printf("%s could not be closed! error %u\n", fname, GetLastError());

            if(DeleteFile(fname) != 0)
              printf("%s file successfully deleted!\n", fname);
            else printf("%s could not be deleted! error %u\n", fname, GetLastError());
            break;
        case 3 :
            //create option
            hFile = CreateFile(fname,               // file to be opened
                                GENERIC_WRITE,      // open for writing
                                FILE_SHARE_WRITE,   // share for writing
                                NULL,               // default security
                                CREATE_NEW,         // create new file only
                                FILE_ATTRIBUTE_NORMAL |FILE_ATTRIBUTE_ARCHIVE | SECURITY_IMPERSONATION,
                                                    // normal file archive and impersonate client
                                NULL);              // no attribute template

            if(hFile == INVALID_HANDLE_VALUE)
              printf("Could not create %s file, error %u.\n", fname, GetLastError());
            else printf("%s file created successfully, error if any, %u.\n", fname, GetLastError());
            break;
        case 4 :
            //open option
            hFile = CreateFile(fname,            // file to create
                      GENERIC_WRITE,             // open for writing
                      FILE_SHARE_WRITE,          // allow write share
                      NULL,                      // default security
                      OPEN_EXISTING,             // opens a file
                      FILE_ATTRIBUTE_NORMAL |FILE_ATTRIBUTE_ARCHIVE | SECURITY_IMPERSONATION,
                      NULL);                     // no attribute template

            if(hFile == INVALID_HANDLE_VALUE)
              printf("Could not open %s file, error %u.\n", fname, GetLastError());
            else printf("%s file opened successfully, error if any, %u.\n", fname, GetLastError());
            break;
        default :
            //error message
            printf("Sorry but %d is not a valid option!", menuOption);
            break;
    }
 } while (menuOption !=0);

  return 0;
}

Thanks,
Gid

I have tried to give the FILE_SHARE_WRITE | READ | DELETE permissions but that seems to error.

If you run the above code it allows you to create file, when you then open file you get a success message. delete then fails. (options 3, 4 then 2)

if instead you just choose (options 3 and 2) it creates successfully and then deletes successfully.

Note: the above was coded and compiled in code::blocks.

Originally Posted by Elysia

Of course you cannot delete it after you've opened it. The same applies to any language, because it's enforced by the OS.
As long as there is an application that has an open handle to the file, you can't delete it.

That would of course depend on the operating systems. Some *nix flavours allow some accounts to delete open files for example.
Handy for truncating logfiles, just delete the file and a well-written server will just create a new one with the same name.

Sorry,

Just to clarify, the delete procedure performs a close on the handle before attempting the delete.
This close succeeds but the subsequent delete fails.

When running this on my system the following options replicate my error.

Select option 3.
Select option 4.
Select option 2.

I am running WinXP sp2.

Cheers,
Gid

From my limited experience it seems to me that one of the following is happening:

1) the code used to open the file (switch case 4) is changing the permissions in some way as to restrict deletion.

2) The code to close the file (switch case 2) that is as follows: if(CloseHandle(hFile) != 0)
Does not actually close the file like it says.

Originally Posted by matsp

Actually, it continues writing to the existing (now invisible) file until the server is restarted (or until it closes and opens the file for some other reason). And as far as I know, it has nothing to do with what account you have - that will only affect what files you can delete, but not whether you can delete one that is open or not.
--
Mats

The contents of the file that existed before are however deleted, so the effect is the same.
Were nothing to be written to the file after the rm command (including a close command) it would be a goner.

Of course the account only determines whether you have delete access at all, just thought to mention it to prevent someone asking why file XXX cannot be deleted by him but YYYY can

Originally Posted by zacs7

> If you can write to open files, it can even be a security risk.
That's what flockfile() is for... Bang supposed security risk gone (I can't even see how there would be one anyway...)

If you could write to an executable that's being read by the operating system at that moment you could inject code in it that would be executed as well.
Potential security risk I guess.

Highly theoretical of course, far better to intercept the process after it's been loaded into memory and been validated as safe by virus scanners and change the instruction sequence there.

are we getting off topic here :-P

Any ideas whether my 2 possible reasons for this error are correct and/or how to resolve?