CreateFile library error

[eoredson]

I have been using this code for awhile. It is a CreateFile library function call.
Problem it work in Qb64pe-32 bit but in 64-bit throws a GNU C++ compilation error and I wanted to know why!?

Erik.

Code: (Select All)

Rem $Dynamic
DefLng A-Z
Declare Dynamic Library "kernel32"
    Function CloseHandle& (ByVal hfile As _Offset)
End Declare

Rem hfind = CreateFileA(ASCIIZ, &H180, &H3, 0, 3, 0, 0)
' parameters:
'  (1) pointer to filename
'  (2) access:
'    x80(128)  - read
'    x100(256) - write
'  (3) sharing
'  (4) security attributes
'  (5) create file flag
'  (6) flags (standard OSHA)
'  (7) pointer to template file

' paramater 5
'  0 DEFAULT_OPEN_EXISTING = open only if exists
'  1 CREATE_NEW    = create only if not exist
'  2 CREATE_ALWAYS = always create new file
'  3 OPEN_EXISTING = open only if exists
'  4 OPEN_ALWAYS  = open file always
'  5 TRUNCATE_EXISTING = open/truncate to 0 only if exists
'  6 OPEN_DIRECTORY    = open if directory exists

Declare Library
    Function CreateFileA& (filename$, Byval access&, Byval sharing&, Byval sec_attr%&, Byval create&, Byval flags&, Byval template%&)
End Declare
Dim hfind As _Offset

' detect file
Print "Enter filename";
Input f$
If Len(f$) Then
    f$ = f$ + Chr$(0)
    hfind = CreateFileA(f$, &H180, 0, 0, 3, 0, 0)
    If hfind Then
        Print "File exists."
        r = CloseHandle(hfind)
    End If
End If
End

[DSMan195276]

'CreateFileA' returns a HANDLE, which should be treated as an `_Offset`, but you wrote it as `CreateFileA&`, so the return value is treated as a 32-bit `LONG`.

The C++ compiler isn't allowing you to make the mistake of casting the HANDLE value to a LONG (which is what QB64 will do to make your function definition work) because that's always a bug on 64-bit systems and chops-off the top-half of the 64-bit HANDLE value, making it useless.

[eoredson]

So if I modify the handle to:

Code: (Select All)

Dim hfind As _Unsigned Long

it should work on 64-bit qb64?

Erik.

[DSMan195276]

So if I modify the handle to:

Code: (Select All)

Dim hfind As _Unsigned Long

it should work on 64-bit qb64?

Erik.

You got it backwards. You correctly declared `hfind` as an `_Offset` type, but you incorrectly declared the return type of `CreateFileA` to be a `Long` instead of an `_Offset`. You need to declare it as `CreateFileA%&` so that QB64 knows it returns an _Offset type.

[eoredson]

Can you tell me if this is correct..

Code: (Select All)

Rem $Dynamic
DefLng A-Z
Declare Dynamic Library "kernel32"
    Function CloseHandle& (ByVal hfile As _Offset)
End Declare

Rem hfind = CreateFileA(ASCIIZ, &H180, &H3, 0, 3, 0, 0)
' parameters:
'  (1) pointer to filename
'  (2) access:
'    x80(128)  - read
'    x100(256) - write
'  (3) sharing
'  (4) security attributes
'  (5) create file flag
'  (6) flags (standard OSHA)
'  (7) pointer to template file

' paramater 5
'  0 DEFAULT_OPEN_EXISTING = open only if exists
'  1 CREATE_NEW    = create only if not exist
'  2 CREATE_ALWAYS = always create new file
'  3 OPEN_EXISTING = open only if exists
'  4 OPEN_ALWAYS  = open file always
'  5 TRUNCATE_EXISTING = open/truncate to 0 only if exists
'  6 OPEN_DIRECTORY    = open if directory exists

Declare Library
    Function CreateFileA%& (filename$, Byval access&, Byval sharing&, Byval sec_attr%&, Byval create&, Byval flags&, Byval template%&)
End Declare
Dim hfind As _Offset

' detect file
Print "Enter filename";
Input f$
If Len(f$) Then
    f$ = f$ + Chr$(0)
    hfind = CreateFileA(f$, &H180, 0, 0, 3, 0, 0)
    If hfind Then
        Print "File exists."
        Print "Handle: "; Hex$(hfind)
        r = CloseHandle(hfind)
    End If
End If
End

If the entire problem is with the function declaration then I have got it wrong the whole time.

[mnrvovrfc]

In 64-bit _UNSIGNED LONG sometimes won't be good enough, and it won't be toward a parameter that expects a pointer. It's because LONG in QB64 is always 32-bit. It needs to be _INTEGER64 or better yet, _OFFSET.

When converting 32-bit code to 64-bit be prepared to turn any LONG or _UNSIGNED LONG into _OFFSET, or less frequently _INTEGER64. But it depends on the context, such as that "size_t" that seems to be declared as different type in each C/C++ header file.

Pointers are really a PITA which is why I gave up soon with C programming. Was repeatedly crashing my computer trying to program a cheap window manager out of the equivalent of SCREEN 0 limited to MS-DOS, many many years ago.

[DSMan195276]

If the entire problem is with the function declaration then I have got it wrong the whole time.

The code looks good to me, and seems to work

Yes it was technically wrong the whole time. The catch is that because `_Offset` is 32-bits wide in 32-bit QB64, and a `Long` is also 32-bits wide, using `CreateFileA&` happens to work anyway when using 32-bit QB64. It's only when using 64-bit QB64 that the `_Offset` vs `Long` distinction matters.

To make your code portable between 32-bit and 64-bit you should ensure you use `_Offset` for any value that needs to vary in size depending on the platform (That goes for all pointer types, such as `HANDLE` in Win32).

[eoredson]

That helps and is a real pita because:

  32-bit = Long/_Unsigned Long
  64-bit = _Integer64/_Offset

never seemed clear to me because of the function declaration is CreateFile%& as well..

Erik.

[eoredson]

My ultimate goal was to make sure my projects are cross-platform compatible between 32-bit and 64-bit.

I can't test this fact since I have no 64-bit version of Qb64pe that ever worked very well..

If I can get around the compilation errors then I can test the code.

[DSMan195276]

That helps and is a real pita because:

  32-bit = Long/_Unsigned Long
  64-bit = _Integer64/_Offset

never seemed clear to me because of the function declaration is CreateFile%& as well..

Erik.

That's note quite right, `_Offset` is not the same thing as `_Integer64`.

`_Offset` is special, it is 32-bits wide on 32-bit QB64, and 64-bits wide on 64-bit QB64. It is a different size depending on the version used, which is also why you need to use it to represent types like `HANDLE` which also differ in size in C++ depending on the platform. To make cross-platform programs you have to use `_Offset` to represent C++ types like pointers which are a different size on different platforms.