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Thread: [RESOLVED] Just found a VB Bug :O ?

  1. #1

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    Frenzied Member some1uk03's Avatar
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    Resolved [RESOLVED] Just found a VB Bug :O ?

    Something strange going on here... Think i just found a VB Bug!

    Can someone run this code and put a REMARK on the If bolFunc = True Then line....
    Although bolFunc is TRUE it still goes to the ELSE part of the IF statement? ***!

    Code:
    Option Explicit
    
    Private Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, ByVal lpProcName As String) As Long
    Private Declare Function GetModuleHandle Lib "kernel32" Alias "GetModuleHandleA" (ByVal lpModuleName As String) As Long
    Private Declare Function GetCurrentProcess Lib "kernel32" () As Long
    Private Declare Function IsWow64Process Lib "kernel32" (ByVal hProc As Long, bWow64Process As Boolean) As Long
    
    
    Private Sub Form_Load()
    MsgBox Is64bit
    End
    End Sub
    Public Function Is64bit() As Boolean
    On Error GoTo errFound
        Dim handle As Long, bolFunc As Boolean
    
        ' Assume initially that this is not a Wow64 process
        bolFunc = False
    
        ' Now check to see if IsWow64Process function exists
        handle = GetProcAddress(GetModuleHandle("kernel32"), "IsWow64Process")
    
        If handle > 0 Then ' IsWow64Process function exists
            ' Now use the function to determine if
            ' we are running under Wow64
            IsWow64Process GetCurrentProcess(), bolFunc
        End If
    
        If bolFunc = True Then
                    Is64bit = True
        Else
                    GoTo errFound
        End If
    Exit Function
    errFound:
    
    End Function
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  2. #2
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    Re: Just found a VB Bug :O ?

    the api call returns 1, vb6 true = -1, so not equal even though the bolfunc= true

    Code:
    if bolfunc then
    i do my best to test code works before i post it, but sometimes am unable to do so for some reason, and usually say so if this is the case.
    Note code snippets posted are just that and do not include error handling that is required in real world applications, but avoid On Error Resume Next

    dim all variables as required as often i have done so elsewhere in my code but only posted the relevant part

    come back and mark your original post as resolved if your problem is fixed
    pete

  3. #3
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    Re: Just found a VB Bug :O ?

    The BOOL type is 32 bits so your "bowlFunct" should really be a Long.

    The entrypoint you call here has no idea you have broken protocol, so when it writes 4 bytes to the 2 bytes you provided for it... something else could get overwritten.

    Some of this may get paved over by the mechanism underlying calls to Declare items but in general it is a poor and dangerous practice to get function signatures wrong.

    BOOL vs. VARIANT_BOOL vs. BOOLEAN vs. bool

  4. #4

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    Frenzied Member some1uk03's Avatar
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    Re: Just found a VB Bug :O ?

    Ok, I do now understand what is going on here..... but

    I still find it a bit strange, as the API is referencing a Boolean [bWOW64Process as Boolean] not a Long.
    Name:  vvb.png
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    Shouldn't that be returning a True Boolean of -1 or 0 in the first place?
    + Doesn't boolean work in a way where 0 is False and anything <> 0 is True [not just -1]?
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  5. #5
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    Re: Just found a VB Bug :O ?

    You are playing a game of "pretend" with a Declare, and here you are pretending to be the wrong thing.

    IsWow64Process just gets an address to write to. It has no idea that you called it some specific VB type.

  6. #6
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    Re: Just found a VB Bug :O ?

    VB6 has no clue about parameters or return type, so it relies on you to provide the correct declaration. BOOL is 32-Bit in the Win32 API, while VB6 Boolean is 16-Bits. In return values, the calling convention uses 32-Bit for return values, and this is done for 32-Bit alignment, so sometimes you might get away with the return value being declared as "Boolean". VB6 in this case throws the upper 16-Bits.

    As far as I know, this won't work with parameters. If the parameters are not declared correctly, then all bets are off, and you get undefined behavior. So, whenever you see BOOL in the API Docs, use "As Long" always.

    See Windows Data Types.
    Last edited by qvb6; Jul 5th, 2019 at 01:34 AM.

  7. #7
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    Re: Just found a VB Bug :O ?

    Quote Originally Posted by some1uk03 View Post
    Shouldn't that be returning a True Boolean of -1 or 0 in the first place?
    It has what the API wrote there.
    The Boolean type could had been done in a way that always ensure 0 or -1 when it returns the value, but that check would take time and would had rendered the Boolean type slower.

    Quote Originally Posted by some1uk03 View Post
    + Doesn't boolean work in a way where 0 is False and anything <> 0 is True [not just -1]?
    Yes, and if you change your line from:

    Code:
    If bolFunc = True Then
    to

    Code:
    If bolFunc Then
    it works.
    Because bolFunc is not equal to True, it is equal to 1. But when evaluated, it is evaluated to True.

    Another workaround would be:

    Code:
    bolFunc = CBool(CInt(bolFunc))
    before the If bolFunc = True Then to convert the 1 to -1

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