Bug or feature? DllClose sets last Windows error to zero

[funkey]

DllClose makes the function _WinAPI_GetLastError() return zero. OK that would not be a problem and I understand why this is as it is. But if I make a DllCall without DLL handle but with DLL name, then DllOpen and DllCose is automatically called. And then _WinAPI_GetLastError() always returns zero. I now use 3.3.8.1 and can not test on newer version, but I think it's the same result.

 

Here is an example:

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#include <WinAPI.au3>

Global Const $tagDATA_BLOB = "DWORD cbData;ptr pbData;"

; DllClose sets last Windows error to zero

_BugTest()
_WorkingTest()

Func _BugTest()
    Local $bData = Binary("0x1234567890")
    Local $tDataBuf = DllStructCreate($tagDATA_BLOB)
    Local $tDataIn = __DataToBlob($bData)
    Local $aRet = DllCall("crypt32.dll", "BOOL", "CryptUnprotectData", "struct*", $tDataIn, "ptr*", 0, "ptr", 0, "ptr", 0, "ptr", 0, "DWORD", 0, "struct*", $tDataBuf)
    If $aRet[0] = 0 Then ;of cource this fails
        MsgBox(16, "BugTest", "Last Windows error: " & _WinAPI_GetLastError())
    Else
        _WinAPI_LocalFree(DllStructGetData($tDataBuf, "pbData"))
    EndIf

    _WinAPI_LocalFree(DllStructGetData($tDataIn, "pbData"))
EndFunc

Func _WorkingTest()
    Local $bData = Binary("0x1234567890")
    Local $tDataBuf = DllStructCreate($tagDATA_BLOB)
    Local $tDataIn = __DataToBlob($bData)
    Local $hDLL_Crypt32 = DllOpen("crypt32.dll")
    Local $aRet = DllCall($hDLL_Crypt32, "BOOL", "CryptUnprotectData", "struct*", $tDataIn, "ptr*", 0, "ptr", 0, "ptr", 0, "ptr", 0, "DWORD", 0, "struct*", $tDataBuf)
;~  DllClose($hDLL_Crypt32)
    If $aRet[0] = 0 Then ;of cource this fails
        MsgBox(16, "WorkingTest", "Last Windows error: " & _WinAPI_GetLastError())
    Else
        _WinAPI_LocalFree(DllStructGetData($tDataBuf, "pbData"))
    EndIf
    DllClose($hDLL_Crypt32)
    _WinAPI_LocalFree(DllStructGetData($tDataIn, "pbData"))
EndFunc


Func __DataToBlob($data)
    ;funkey 2014.08.11th
    Local $iLen, $tDataIn, $tData, $aMem
    Local Const $LMEM_ZEROINIT = 0x40
    Select
        Case IsString($data)
            $iLen = StringLen($data)
        Case IsBinary($data)
            $iLen = BinaryLen($data)
        Case Else
            Return SetError(1, 0, 0)
    EndSelect

    $tDataIn = DllStructCreate($tagDATA_BLOB)
    $aMem = DllCall("Kernel32.dll", "handle", "LocalAlloc", "UINT", $LMEM_ZEROINIT, "UINT", $iLen)
    $tData = DllStructCreate("byte[" & $iLen & "]", $aMem[0])

    DllStructSetData($tData, 1, $data)
    DllStructSetData($tDataIn, "cbData", $iLen)
    DllStructSetData($tDataIn, "pbData", DllStructGetPtr($tData))

    Return $tDataIn
EndFunc   ;==>__DataToBlob

What do you think about it?

[Jon]

GetLastError is pretty useless outside of a native C++ program. AutoIt calls internal windows functions all the time so you are never going to get anything useful out of it...

[funkey]

GetLastError is used everywhere in the WinAPI-UDF. But I found out, that there is no problem if the dll is already used by AutoIt internally (see sample code).

Can't we store the last error after function call and then set it after closing dll handle before returning to script? This would give the expected behaviour with winapi dll calls.

#include <WinAPI.au3>

Global $hFile = 0 ;invalid file pointer

Global $iRes = _WinAPI_SetFilePointer($hFile, 1, 2)
If $iRes = $INVALID_SET_FILE_POINTER Then
    ConsoleWrite("Last Windows error: " &  _WinAPI_GetLastError() & @LF)    ; 6 = ERROR_INVALID_HANDLE
EndIf

Global $hDllKernel32 = DllOpen("kernel32.dll")
Global $iRes2 = _Winapi_SetFilePointerViaDllHandle($hDllKernel32, $hFile, 1, 2)
DllClose($hDllKernel32)
If $iRes = $INVALID_SET_FILE_POINTER Then
    ConsoleWrite("Last Windows error: " &  _WinAPI_GetLastError() & @LF)    ; 6 = ERROR_INVALID_HANDLE
EndIf


Func _WinAPI_SetFilePointerViaDllHandle($hDLL, $hFile, $iPos, $iMethod = 0)
    Local $aResult = DllCall($hDLL, "INT", "SetFilePointer", "handle", $hFile, "long", $iPos, "ptr", 0, "long", $iMethod)
    If @error Then Return SetError(@error, @extended, -1)
    Return $aResult[0]
EndFunc   ;==>_WinAPI_SetFilePointer