Hi,
I’m trying to rewrite the following code from
https://sjohannes.wordpress.com/2012/03/23/win32-python-getting-all-window-titles/
from Python to Julia
import ctypes
EnumWindows = ctypes.windll.user32.EnumWindows
EnumWindowsProc = ctypes.WINFUNCTYPE(ctypes.c_bool, ctypes.POINTER(ctypes.c_int), ctypes.POINTER(ctypes.c_int))
GetWindowText = ctypes.windll.user32.GetWindowTextW
GetWindowTextLength = ctypes.windll.user32.GetWindowTextLengthW
IsWindowVisible = ctypes.windll.user32.IsWindowVisible
titles = []
def foreach_window(hwnd, lParam):
if IsWindowVisible(hwnd):
length = GetWindowTextLength(hwnd)
buff = ctypes.create_unicode_buffer(length + 1)
GetWindowText(hwnd, buff, length + 1)
titles.append(buff.value)
return True
EnumWindows(EnumWindowsProc(foreach_window), 0)
print(titles)
The code lists titles of all currently visible windows.
I’m struggling with how to specify the stdcall calling convention for the callback function. In a simple ccall one can specify the calling convention
tickCount = ccall( (:GetTickCount, "kernel32"), stdcall, UInt32, () )
but for callback, the function pointer created by cfunction
has no calling convention property. Is such functionality available?
Cheers,
Petr
No, calling convention specification is not supported for cfunction
. But calling conventions are unified on 64-bit Windows so this won’t matter unless you are on 32-bit Windows.
see also: stdcall with cfunction? · Issue #5613 · JuliaLang/julia · GitHub
@ihnorton Thank you for the explanation. Still my attempt crashes julia:
function foreach_window{T}(hwnd::T, lParam::T)
return convert(Cint, 1)::Cint
end
const windowEnumCallback = cfunction(foreach_window, Cint, (Ref{Cint}, Ref{Cint}))
ccall((:EnumWindows, "User32"), stdcall, Cint, (Ptr{Void}, Ptr{Cint}), windowEnumCallback, Ref{Cint}(0))
the signatures are
Enumerates all top-level windows on the screen by passing the handle to each window, in turn, to an application-defined callback function. EnumWindows continues until the last top-level window is enumerated or the callback function returns FALSE.
BOOL WINAPI EnumWindows(
_In_ WNDENUMPROC lpEnumFunc,
_In_ LPARAM lParam
);
BOOL CALLBACK EnumWindowsProc(
_In_ HWND hwnd,
_In_ LPARAM lParam
);
Please review the C interface section of the manual. There are a few problems, such as:
the cfunction
signature must match the function declaration
Ref
is Julia-owned memory, so it doesn’t make sense in the cfunction
signature
foreach_window
should not be parameterized by type ({T}
)
passing a Ref{Cint}(0)
to EnumWindows
doesn’t make sense – it’s just a long.
The code below works; hopefully enough to get you going:
typealias HANDLE Ptr{Void}
typealias LPARAM Clong
handles = HANDLE[]
function foreach_window(hwnd::HANDLE, lParam::LPARAM)
push!(handles, hwnd)
return convert(Cint, 1)::Cint
end
const windowEnumCallback = cfunction(foreach_window, Cint, (HANDLE, LPARAM))
ccall((:EnumWindows, "User32"), stdcall, Cint, (Ptr{Void}, LPARAM), windowEnumCallback, 0)
(I have some old demo code here that might be helpful – although I have no idea if it works at all in current Julia)
Works great, thank you Isaiah. Making clarification in manual.