help with simple C-to-PB port - its finished, but somethings not right

[Wayne Diamond]

I'm trying to port some simple C++ code over to PB. It uses file-mapping, and according to POFFS2, nobody has used the OpenEvent() API call before!
Here is the code - very simple:

	HANDLE hEventGuard = OpenEvent(EVENT_ALL_ACCESS, FALSE, PB_EVENT_NAME);
	HANDLE hFileMapping = OpenFileMapping(FILE_MAP_READ, FALSE, PB_NAME);
	if(hEventGuard == NULL | | hFileMapping == NULL)
	{
		printf("Error: \n");
		CloseHandle(hEventGuard);
		CloseHandle(hFileMapping);
		return;
	}

I was able to port it over, but the call to OpenEvent() from PB keeps returning %NULL - 0
Does anybody know why? Here is my port:

%EVENT_ALL_ACCESS = &H001F0003
hEventGuard = OpenEvent(%EVENT_ALL_ACCESS, %FALSE, PB_EVENT_NAME)
hFileMapping = OpenFileMapping(%FILE_MAP_READ, %FALSE, PB_NAME)
STDOUT "hEventGuard=" & STR$(hEventGuard)   'always returns 0
STDOUT "hFileMapping=" & STR$(hFileMapping) 'also returns 0 because the call to OpenEvent failed
CloseHandle hEventGuard
CloseHandle hFileMapping

Is the win32api.inc declaration ok? -

DECLARE FUNCTION OpenEvent LIB "KERNEL32.DLL" ALIAS "OpenEventA" (BYVAL dwDesiredAccess AS LONG, BYVAL bInheritHandle AS LONG, lpName AS ASCIIZ) AS LONG

Here is MS VC6's declaration:

WINBASEAPI
HANDLE
WINAPI
OpenEventA(
    DWORD dwDesiredAccess,
    BOOL bInheritHandle,
    LPCSTR lpName
    );
WINBASEAPI
HANDLE
WINAPI
OpenEventW(
    DWORD dwDesiredAccess,
    BOOL bInheritHandle,
    LPCWSTR lpName
    );
#ifdef UNICODE
#define OpenEvent  OpenEventW
#else
#define OpenEvent  OpenEventA
#endif // !UNICODE

Im using NT4 and Win2K so I have a feeling I should be calling the Unicode version of OpenEvent (which isn't defined)
Any help is much appreciated!


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[Tom Hanlin]

Looks ok. Did you check GetLastError?

OpenEventW is the Unicode definition, but I'm not clear why you want Unicode here?


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Tom Hanlin
PowerBASIC Staff

[Peter Lameijn]

Did you use CreateEvent before trying OpenEvent? (Or else OpenEvent will fail and return 0)

------------------
Peter.
mailto[email protected][email protected]</A>

[Wayne Diamond]

There's a pre-compiled C DLL that is an always-running base provider. I dont believe I need to call CreateEvent, as the event is created by the DLL not my program. My program just needs to open and read from the shared memory map
Ive got demo source showing how to call it, and this is how it starts:

#define THE_EVENT_NAME		TEXT("TheSharedEvent")
 
void _cdecl mainCRTStartup(void)
{
	HANDLE hEventGuard = OpenEvent((EVENT_ALL_ACCESS, FALSE, THE_EVENT_NAME);
}

So as soon as it starts, it immediately calls OpenEvent, and it works! OpenEvent returned a number (84 in this instance) according to the C version, but keeps returning 0 when I call it from PB, I dont understand why
If I can get the call to OpenEvent working, then the call immediately below it to OpenFileMapping should also work which will solve all my problems

Thankyou!


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[Peter Lameijn]

Normally a few things can cause this:

1) The event name isn't correct (case sensitive!)
2) The event isn't created yet by CreateEvent.
3) Something with the access rights isn't ok

GetLastError should tell you what it is....

------------------
Peter.
mailto[email protected][email protected]</A>

[Wayne Diamond]

GetLastError = 2
Error Description = "The system cannot find the file specified."

1) The event name isn't correct (case sensitive!)
Its correct
2) The event isn't created yet by CreateEvent.
The event is definately created
3) Something with the access rights isn't ok
Im logged in as administrator so I should be able to obtain proper access

Im spelling it correctly - case sensitively, Ive defined it as an ASCIIZ * 50
any ideas ?



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[Peter Lameijn]

If GetLastError returns 2 (ERROR_FILE_NOT_FOUND) then the kernel object with the specified
name does not exist.
Following example should work. If you start it several times, only the first one should
create an event, the rest should open the event...

#Compile Exe
#Include "win32api.inc"
%EVENT_ALL_ACCESS = &h0001F0003

Function PbMain() As Long
  Local lRet As Long, lError As Long, lEventName As Asciiz * %MAX_PATH
  lEventName = "TestEvent"
  lRet = CreateEvent (ByVal %Null, %False, %False, lEventName)
  lError =  GetLastError ()
  If IsFalse lRet Then
    MsgBox "Unable to create Event, error:" + Str$(lError),,"CreateEvent error"
  Else
    If lError = %ERROR_ALREADY_EXISTS Then
      lRet = OpenEvent(ByVal %EVENT_ALL_ACCESS, %False, lEventName)
      lError = GetLastError()
      If lRet Then
        MsgBox "Opened existing Event, handle:" + Str$(lRet),,"OpenEvent:"
      Else
        MsgBox "Unable to open Event, error:" + Str$(lError),,"OpenEvent error" : Exit Function
      End If
    Else
      MsgBox "Created new Event, handle:" + Str$(lRet),,"CreateEvent:"
    End If
  End If
End Function

------------------
Peter.
mailto[email protected][email protected]</A>



[This message has been edited by Peter Lameijn (edited October 16, 2001).]

[Wayne Diamond]

[problem solved]

Strewth, its working! Im not sure why though , something very subtle was obviously out. Ive tried to re-break it and now I can't, it just keeps working, sheesh
Anyway Peter the minor mods I made were based on your code below so thanks very much, Ive never done any file mapping before, it should be interesting!
Cheers


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