How to get control text? - windows

I want to get control text. but this code return parent class name.
const wchar_t* textInput = L"Login";
HWND btnHandle = CreateWindowEx(0, L"BUTTON", textInput, WS_CHILD | WS_VISIBLE | BS_DEFPUSHBUTTON,
mCoordinate.x, mCoordinate.y, mDimension.cx, mDimension.cy, parentHandle, NULL,
(HINSTANCE)GetWindowLongPtr(parentHandle, GWLP_HINSTANCE), NULL);
wchar_t* textOutput;
int length = GetWindowTextLengthW(btnHandle);
GetWindowText(btnHandle, textOutput, length);
MessageBox(NULL, textOutput, L"Window Text", MB_OK);

As documented, the lpString argument to GetWindowTextW is:
The buffer that will receive the text.
The API does not provide that buffer for you. Instead, you will have to pass it in, as illustrated here:
size_t length{ GetWindowTextLengthW(btnHandle) };
// Allocates a buffer for `length` characters plus a NUL terminator
std::wstring text(length, L'\0');
// The API promises to write a NUL terminator into the final character
// so it is safe to lie about the length
length = GetWindowTextW(btnHandle, text.data(), text.size() + 1);
// Resize in case we got less than promised
text.resize(length);
MessageBoxW(NULL, text.c_str(), L"Window Text", MB_OK);

Related

Duration of the busy cursor when launching a Windows desktop application

When you launch a Windows desktop application, the system changes the arrow to one with an animated busy spinner (presumably from IDI_ARROW to IDI_APPSTARTING). Once the application presents a window, the cursor is restored to indicate that it's ready for input.
With my own Win32 applications, the spinner continues for several (5?) seconds, even though the main window is fully rendered and ready for interaction. It was my understanding that the spinner vanishes once the just-launched program started pumping messages. More specifically, I thought it used the same criteria as WaitForInputIdle.
Since Windows 10, however, some applications, including ones I've written, appear to be stuck with the busy cursor for the duration of the timeout—even beyond the moment that the application becomes responsive to mouse and keyboard input.
What should I do in my programs to let the system know that initialization is complete and the spinner is no longer needed?
UPDATE: The problem occurs only when launching the application from the keyboard (like a CMD prompt, the Run window, or using the keyboard to launch the process in the debugger in Visual Studio). If you double-click the program with the mouse, the spinner vanishes quickly, as expected.
UPDATE 2: Given that others cannot repro, my best guess is that there's a buggy driver involved. Thanks to everyone who helped brainstorm in the comments.
Self-contained repro below.
#include <Windows.h>
LRESULT OnPaint(HWND hwnd, UINT, WPARAM, LPARAM) {
PAINTSTRUCT ps;
::BeginPaint(hwnd, &ps);
RECT rc;
::GetClientRect(hwnd, &rc);
::DrawTextW(ps.hdc, L"Hello, World", -1, &rc,
DT_SINGLELINE | DT_CENTER | DT_VCENTER | DT_NOPREFIX);
::EndPaint(hwnd, &ps);
return 0;
}
LRESULT MyWindowProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
switch (msg) {
case WM_DESTROY: ::PostQuitMessage(0); break;
case WM_PAINT: return OnPaint(hwnd, msg, wp, lp);
}
return ::DefWindowProcW(hwnd, msg, wp, lp);
}
int WinMain(HINSTANCE hinst, HINSTANCE, LPSTR, int nShowCmd) {
WNDCLASSW wc = {0};
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = MyWindowProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hinst;
wc.hIcon = NULL;
wc.hCursor = ::LoadCursorW(NULL, IDC_ARROW);
wc.hbrBackground = ::GetSysColorBrush(COLOR_WINDOW);
wc.lpszMenuName = nullptr;
wc.lpszClassName = L"My Very Own Window Class";
const ATOM atomClass = ::RegisterClassW(&wc);
if (atomClass == 0) return ::GetLastError();
// Ugly cast for WinAPI's legacy type punning.
const LPCWSTR wndclass =
reinterpret_cast<LPCWSTR>(static_cast<UINT_PTR>(atomClass));
const HWND hwnd =
::CreateWindowW(wndclass, L"Test", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT,
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL,
NULL, hinst, nullptr);
if (hwnd == NULL) return ::GetLastError();
::ShowWindow(hwnd, nShowCmd);
MSG msg = {0};
while (::GetMessageW(&msg, NULL, 0, 0) > 0) {
::TranslateMessage(&msg);
::DispatchMessageW(&msg);
}
return (msg.message == WM_QUIT) ? static_cast<int>(msg.wParam) : 1;
}
What should I do in my programs to let the system know that initialization is complete and the spinner is no longer needed?
There seems to be agreement that the spinner should vanish once the application has started pumping messages and has no pending input events queue.
The fact that's not working in all cases for me is likely a local issue, like a buggy driver spamming the input queue (which somehow never make it to window messages). There's not much point in hashing that out here on SO, so I'm putting up this community wiki answer and moving on.

Going Fullscreen in win32 without 2 WM_SIZE message

So I am creating a fullscreen function in win32 c++ doing:
uint8_t isFullscreen = 0;
RECT winRect; //Current Window Rect
RECT nonFullScreenRect; //Rect Not In Full Screen Position (used to restore window to not full screen position when coming out of fullscreen)
uint32_t screen_width = DEFAULT_SCREEN_WIDTH;
uint32_t screen_height = DEFAULT_SCREEN_HEIGHT;
void Fullscreen( HWND WindowHandle )
{
isFullscreen = isFullscreen ^ 1;
if( isFullscreen )
{
//saving off current window rect
nonFullScreenRect.left = winRect.left;
nonFullScreenRect.right = winRect.right;
nonFullScreenRect.bottom = winRect.bottom;
nonFullScreenRect.top = winRect.top;
SetWindowLongPtr( WindowHandle, GWL_STYLE, WS_POPUP | WS_CLIPCHILDREN | WS_CLIPSIBLINGS | WS_VISIBLE ); //causes a resize msg
HMONITOR hmon = MonitorFromWindow(WindowHandle, MONITOR_DEFAULTTONEAREST);
MONITORINFO mi = { sizeof( mi ) };
GetMonitorInfo( hmon, &mi );
screen_width = mi.rcMonitor.right - mi.rcMonitor.left;
screen_height = mi.rcMonitor.bottom - mi.rcMonitor.top;
MoveWindow( WindowHandle, mi.rcMonitor.left, mi.rcMonitor.top, (int32_t)screen_width, (int32_t)screen_height, FALSE );
}
else
{
SetWindowLongPtr( WindowHandle, GWL_STYLE, WS_OVERLAPPEDWINDOW | WS_VISIBLE );
screen_width = nonFullScreenRect.right - nonFullScreenRect.left;
screen_height = nonFullScreenRect.bottom - nonFullScreenRect.top;
MoveWindow( WindowHandle, nonFullScreenRect.left, nonFullScreenRect.top, (int32_t)screen_width, (int32_t)screen_height, FALSE );
}
}
However when it goes fullscreen, the function generates 2 WM_SIZE messages. While when it goes windowed, it generates only 1.
Why is that the case? And how can I make it generate only 1 WM_SIZE message for the proper full screen size?
How can I update an HWND's style and position atomically? asks about it but no one answers it
The reasons I need this is because I am using DirectX12 and on WM_SIZE I wait for all the signals at the end of the command queues before resizing all the swap chain back buffers. And I don't want to have to resize the swap chain twice when switching to fullscreen mode.
case WM_SIZE:
{
screen_width = LOWORD( LParam );
screen_height = HIWORD( LParam );
//DirectX stuff here
}break;
Thanks in advance!
Updated Answer:
The Win32 API allows you to modify parameters of the window one at a time. When a parameter is modified, the API may or may not update the window and trigger a WM_SIZE that will be the size of the window given the current parameters.
Since to have a complete full screen window you need to make at least 2 calls, one to update GWL_STYLE and another to update GWL_EXSTYLE, you have a big chance of getting 2 WM_SIZE calls. One of them will give you the window size without the menu, and the other the full screen window size. It depends in which order you call SetWindowLongPtr, but you'll probably get 2 WM_SIZE and only the second one is "correct", i.e. the one you want in the end.
The more reliable solution to your problem is to use a variable at the top of Main.cpp:
int isTogglingFullScreen = false;
Then inside your full screen toggle code (note where isTogglingFullScreen is being set):
case WM_SYSKEYDOWN:
if (wParam == VK_RETURN && (lParam & 0x60000000) == 0x20000000)
{
// Implements the classic ALT+ENTER fullscreen toggle
if (s_fullscreen)
{
isTogglingFullScreen = true;
SetWindowLongPtr(hWnd, GWL_STYLE, WS_OVERLAPPEDWINDOW);
isTogglingFullScreen = false;
SetWindowLongPtr(hWnd, GWL_EXSTYLE, 0);
int width = 800;
int height = 600;
if (game)
game->GetDefaultSize(width, height);
SetWindowPos(hWnd, HWND_TOP, 0, 0, width, height, SWP_NOMOVE | SWP_NOZORDER | SWP_FRAMECHANGED);
ShowWindow(hWnd, SW_SHOWNORMAL);
}
else
{
isTogglingFullScreen = true;
SetWindowLongPtr(hWnd, GWL_EXSTYLE, WS_EX_TOPMOST);
SetWindowLongPtr(hWnd, GWL_STYLE, WS_POPUP);
SetWindowPos(hWnd, HWND_TOP, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
isTogglingFullScreen = false;
ShowWindow(hWnd, SW_SHOWMAXIMIZED);
}
s_fullscreen = !s_fullscreen;
}
break;
Finally, inside WM_SIZE, change
else if (!s_in_sizemove && game)
{
game->OnWindowSizeChanged(LOWORD(lParam), HIWORD(lParam));
}
to
else if (!s_in_sizemove && game && !isTogglingFullScreen)
{
game->OnWindowSizeChanged(LOWORD(lParam), HIWORD(lParam));
}
This will give you a single call to OnWindowSizeChanged() when you toggle full screen, and the call will be with the correct final size.
--
Old Answer:
If you only want a single WM_SIZE to trigger, when you switch to full screen then you should go for something like this:
SetWindowLongPtr(hWnd, GWL_EXSTYLE, WS_EX_TOPMOST);
SetWindowPos(hWnd, HWND_TOP, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
ShowWindow(hWnd, SW_SHOWMAXIMIZED);
Any SetWindowLongPtr call to GWL_STYLE will trigger a WM_SIZE, so make sure it's only called with GWL_EXSTYLE. For example, if you both set GWL_EXSTYLE to what you want, and reset GWL_STYLE to 0, you'll trigger WM_SIZE twice.
To make it clearer:
Don't use GWL_STYLE in SetWindowLongPtr because it triggers a useless WM_SIZE
ShowWindow will trigger WM_SIZE
The above code will ultimately only trigger WM_SIZE once.
It turns out that YMMV. It's entirely possible that the first time you switch fullscreen, you'll get 2 WM_SIZE. One will be with the original size, and the other with the new size. Subsequent calls will trigger only one WM_SIZE.
Hence, the really bulletproof solution (which I was using anyway before playing around with the SetWindowLongPtr to answer this question, is to validate that the window size has actually changed. Because one thing that I can guarantee in the above call is that you'll never get more than 1 call with the new size. At most you'll get a WM_SIZE call with the old size, which you'll discard by checking that it's the same as the current size.
If you use the DevicesResources template for DX12, you'll see that there's a check in OnWindowSizeChanged() that does nothing if the size hasn't changed.

Why ComboBox does not set and get ItemData in a loop?

I want to save a 'username' and 'ID' in a ComboBox in visual Studio 2010 and WIN32 (c++). Following code is for setting itemdata to combobox:
HWND hCB;
hCB = CreateWindowEx(0, L"COMBOBOX", 0x00,
CBS_DROPDOWNLIST | CBS_HASSTRINGS | CBS_NOINTEGRALHEIGHT | WS_CHILD | WS_VISIBLE | WS_VSCROLL,
10, 10, 200, 100,
hWnd, NULL, (HINSTANCE) GetWindowLong(hWnd, GWL_HINSTANCE), NULL);
WCHAR sTemp[256];
for (int i =0 ; i<4 ; i++)
{
wsprintf(sTemp, L"%s%d", L"User", i);
SendMessage(hCB, CB_ADDSTRING, 0, (LPARAM) sTemp);
wsprintf(sTemp, L"%s%d", L"ID", i);
SendMessage(hCB, CB_SETITEMDATA, (WPARAM)i, (LPARAM)sTemp);
}
And code for getting itemdata from combobox is:
WCHAR *sTemp;
for (int i=0; i < 4 ; i++)
{
sTemp = (WCHAR *)SendMessage(hCB, CB_GETITEMDATA, (WPARAM)i, 0);
MessageBox(NULL, sTemp, NULL, MB_OK);
}
The problem is, MessageBox does not show anything.
When I checked the first part of code by adding a CB_GETITEMDATA message for each combobox item, and a MessageBox to show result, I've found that all values of items' itemdata is "ID3", that is the last itemdata in the list.
I think the codes are straightforward, But I can't find what wrong is with my code?
You set the items' data to a pointer to the sTemp temporary string (the same for all items by the way).
When that variable goes out of scope, the pointer becomes invalid, and de-referencing it may cause a crash.
P.S. Just noticed your last comment. If you do it in the same scope, the sTemp contains the last text you wsprintf'ed to it, and every item points to it.
[added]
If you want to add string data to each item in your ComboBox, you need to allocate those strings. For example:
char* p = new char[some_buffer_length];
Then use that p in your call to set item data.
Don't forget to free the memory when you are done by calling:
delete [] p;
for each of your items.

Win32- Getting ListView Control content from another application

I am trying to access the ListView control (located within an Dialog) in another application, and get the data from within the control. Here is the Win32 code (with appropiate comments) that I am writing :
HWND hListView32 = hRoot; //HANDLE to the ListView control within the Dialog, having class name - "SysListView32"
int cnt = (int) ::SendMessage(hListView32, LVM_GETITEMCOUNT, 0, 0L); //returns CORRECT item count of the ListView Control
int nItem=0,nRes;
for(int nItem=0;nItem<cnt;nItem++)
{
LVITEM LvItem; // ListView Item struct
char Text[255]={0};
char Temp[255]={0};
char Temp1[255]={0};
memset(&LvItem,0,sizeof(LvItem));
LvItem.mask=LVIF_TEXT;
LvItem.iSubItem=1; //Trying to get the 2nd Colomn text
LvItem.pszText=Text; //Does not returns any Text, after the below SendMessage is executed???
LvItem.cchTextMax=256;
LvItem.iItem=nItem;
nRes = (int)::SendMessage(hListView32,LVM_GETITEMTEXT, nItem, (LPARAM)&LvItem);
DWORD dd = ::GetLastError(); //returns 0
}
Though the code is executing, I am not getting any data from within the control. However, I am able to retrieve the correct Item count from within the control, but no data.
Another approach maybe would be to use an MSAA hook to get the data. But that would be a very long and cumbersome process. Running out of ideas here. Pls help.
Thanks,
There a few possibilities.
DLL Injection Using windows hooks. Pros: simple and straight forward. Cons: many processes get this dll loaded.
DLL Injection Making process to load library by opening it for debugging, allocating a chunc of virtual memory using VallocEx in the context of this process, writing it's memory with WriteProcessMemory and creating a remote thread with start address of LoadLibrary function. Pros: a single process is affected. Cons: A bit more complex than hooks solution.
Read of process memory. Same as option 2 but instead of writing this memory and executing the code remotely, send the message LVM_GETITEMTEXT to the window in question providing a valid known memory location and then read that location with ReadProcessMemory.
ListView messages that pass around buffers only work within the address space of the process that owns the ListView. You will have to use VirtualAllocEx() to allocate a memory block within that same process, then you can write to it with WriteProcessMemory() and have the ListView fill it as needed, then you can read it with ReadProcessMemory() and deallocate it with VirtualFreeEx().
Try this (error handling omitted for brevity):
HWND hListView32 = hRoot;
int cnt = (int) ::SendMessage(hListView32, LVM_GETITEMCOUNT, 0, 0);
if (cnt > 0)
{
DWORD dwProcessId;
GetWindowThreadProcessId(hListView32, &dwProcessId);
HANDLE hProcess = OpenProcess(PROCESS_VM_READ | PROCESS_VM_WRITE | PROCESS_VM_OPERATION, FALSE, dwProcessId);
LVITEM *pLvItem = (LVITEM*) VirtualAllocEx(hProcess, NULL, sizeof(LVITEM), MEM_COMMIT, PAGE_READWRITE);
LPTSTR pText = (LPTSTR) VirtualAllocEx(hProcess, NULL, sizeof(TCHAR)*256, MEM_COMMIT, PAGE_READWRITE);
for(int nItem = 0; nItem < cnt; ++nItem)
{
TCHAR Text[256] = {0};
LVITEM LvItem = {0};
LvItem.mask = LVIF_TEXT;
LvItem.iSubItem = 1;
LvItem.pszText = pText;
LvItem.cchTextMax = 256;
LvItem.iItem = nItem;
WriteProcessMemory(hProcess, pLvItem, &LvItem, sizeof(LVITEM), NULL);
int nRes = (int) ::SendMessage(hListView32, LVM_GETITEMTEXT, nItem, (LPARAM)pLvItem);
if (nRes > 0)
ReadProcessMemory(hProcess, pText, &Text[0], sizeof(TCHAR)*nRes, NULL);
// use Text as needed...
}
VirtualFreeEx(hProcess, pText, 0, MEM_RELEASE);
VirtualFreeEx(hProcess, pLvItem, 0, MEM_RELEASE);
CloseHandle(hProcess);
}
I copypasted code by Remy Lebeau, but it is working very strange in my particular case. The number of elements is retreived correctly via SendMessage(listview, LVM_GETITEMCOUNT, 0, 0)
, but the cycle reads jast the same element every time! It is not the first or last element, not the selected, but seems to be random. Here is my code:
HWND win=FindWindowEx(NULL, NULL, _("TEventLogView"), NULL);
HWND listview=FindWindowEx(win, NULL, _("TListView"), NULL);
int cnt = (int) ::SendMessage(listview, LVM_GETITEMCOUNT, 0, 0);
if (cnt > 0)
{
DWORD dwProcessId;
GetWindowThreadProcessId(listview, &dwProcessId);
int n = grdEvents->GetNumberRows();
HANDLE hProcess = OpenProcess(PROCESS_VM_READ | PROCESS_VM_WRITE | PROCESS_VM_OPERATION, FALSE, dwProcessId);
LVITEM *pLvItem = (LVITEM*) VirtualAllocEx(hProcess, NULL, sizeof(LVITEM), MEM_COMMIT, PAGE_READWRITE);
LPTSTR pText = (LPTSTR) VirtualAllocEx(hProcess, NULL, sizeof(TCHAR)*255, MEM_COMMIT, PAGE_READWRITE);
for(int nItem = 0; nItem < cnt; ++nItem)
{
// need to read 1 - 3 subitems
for (int j = 1; j < 4; j++)
{
TCHAR Text[255] = {0};
LVITEM LvItem = {0};
LvItem.mask = LVIF_STATE | LVIF_TEXT;
LvItem.pszText = pText;
LvItem.cchTextMax = sizeof(TCHAR)*255;
LvItem.iItem = nItem;
LvItem.iSubItem = j;
int nRes1 = WriteProcessMemory(hProcess, pLvItem, &LvItem, sizeof(LVITEM), NULL);
int nRes2 = (int) ::SendMessage(listview, LVM_GETITEMTEXT, (WPARAM)nItem, (LPARAM)pLvItem);
if (nRes2 > 0)
{
ReadProcessMemory(hProcess, pText, &Text[0], sizeof(TCHAR)*nRes2, NULL);
// insert into wxWidgets grid
grdEvents->SetCellValue(nItem, j - 1, Text);
}
}
VirtualFreeEx(hProcess, pText, 0, MEM_RELEASE);
VirtualFreeEx(hProcess, pLvItem, 0, MEM_RELEASE);
CloseHandle(hProcess);
}
}

How to fix garbled text with using WriteFile on a pipe?

I have a Win32 application that I'm making, and it sends a string from one process to another via a named pipe. However, the process that calls ReadFile on the pipe gets the string with some garbled data in it. It returns the number of bytes written correctly, but the last 8 characters or so of the string are garbled.
Here is the code for creating the pipe, and writing to it:
myPipe = CreateNamedPipe(L"\\\\.\\pipe\\testpipe", PIPE_ACCESS_OUTBOUND, PIPE_NOWAIT, 10, 512, 512, 10, NULL);
TCHAR title[128];
GetWindowText(foundHwnd, title, 128);
wstring windowTitle(title);
vector<wstring> splitVec;
boost::split(splitVec, windowTitle, boost::algorithm::is_any_of(wstring(L"|")));
WriteFile(myPipe, splitVec[0].c_str(), splitVec[0].size(), &wrote, NULL);
And here is the code that reads it:
if (WaitNamedPipe(L"\\\\.\\pipe\\testpipe", 5000) == 0) {
MessageBox(NULL, L"Unable to wait for pipe", L"Error", MB_OK);
return false;
}
myPipe = CreateFile(L"\\\\.\\pipe\\testpipe", GENERIC_READ, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if (myPipe == INVALID_HANDLE_VALUE) {
MessageBox(NULL, L"Unable to open pipe", L"Error", MB_OK);
return false;
}
// Other code here...
TCHAR buf[512];
DWORD read;
success = ReadFile(myPipe, buf, 512, &read, NULL);
if (read > 0)
MessageBox(NULL, buf, L"Got Data", MB_OK);
When MessageBox is shown, the end of the string is garbled and I have no idea why. Any ideas?
Thanks!
I think the key here is to make sure that your strings are null terminated and that you send the termination character as well. You shouldn't have to send the entire buffer if the communications is synchronous or if you set it up in PIPE_READMODE_MESSAGE. ReadFile will return when either the specified number of bytes has been read or a write operation completes on the other end of the pipe. I believe that the "garbled" text is really garbage in the read buffer on the client side of the pipe and because you are not transmitting the string termination character, it is including this in the text sent to the message box. Either clear your read buffer before sending or send the string termination character with the message and I think it will work without the overhead of sending a full buffer.
Here is sample client from MSDN. Note how the client sends exactly the number of characters in the message + 1 (including the termination character) and receives into a fixed buffer of size 512. If you look at a server example, you'll see the same pattern.
Some observations on the code you posted:
You need to either 1) explicitly send the null terminated byte, or 2) append one to the data you read.
Since you are reading 512 bytes, you should also be sending exactly 512 bytes.
You can send variable length strings instead by first sending the size of the string, and then sending that many bytes. That way when you read the data you will know how many bytes to read for the actual string.
The problem with what you did will be seen as soon as you send 2 things over the pipe, and you read past what you really want in the first read.
If you are only sending 1 thing over the pipe, you can keep your code, but send size() + 1 when you write to the pipe.
ReadFile / WriteFile were meant to send binary data, not necessarily strings. So you can make a function called ReadString and WriteString that implements my suggestion about reading/writing first the size then the actual string.
Try something like this:
Here is the code for creating the pipe, and writing to it:
myPipe = CreateNamedPipe(L"\\\\.\\pipe\\testpipe", PIPE_ACCESS_OUTBOUND, PIPE_NOWAIT, 10, 512, 512, 10, NULL);
TCHAR title[128];
GetWindowText(foundHwnd, title, 128);
WriteFile(myPipe, title, 128*sizeof(TCHAR), &wrote, NULL);//<---In this case we are sending a null terminated string buffer.
And here is the code that reads it:
if (WaitNamedPipe(L"\\\\.\\pipe\\testpipe", 5000) == 0) {
MessageBox(NULL, L"Unable to wait for pipe", L"Error", MB_OK);
return false;
}
myPipe = CreateFile(L"\\\\.\\pipe\\testpipe", GENERIC_READ, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if (myPipe == INVALID_HANDLE_VALUE) {
MessageBox(NULL, L"Unable to open pipe", L"Error", MB_OK);
return false;
}
// Other code here...
TCHAR buf[128];
DWORD read;
success = ReadFile(myPipe, buf, 128*sizeof(TCHAR), &read, NULL);
if (read > 0)
MessageBox(NULL, buf, L"Got Data", MB_OK);
I ran into this problem with "garbage in the pipe" when writing a generic function to read stdout from any process executed at the command prompt. Therefore, I couldn't alter what was being written to the pipe (as is commonly suggested), I could only alter the read side. So, I "cheated".
If the pipe data didn't end in a null terminator, I replaced the last char with one! It seemed to work for me. I saw this work perfectly where there were nulls and where there were not at the end of my data chunks.
I worried that I might lose a critical last char (and it's possible that you might!), but for my immediate purposes, that didn't happen. You might consider adding a null rather than replacing the end under some circumstances...
Here's code snippit:
const unsigned int MAX_PIPE_PEEKS = 100;
DWORD bytesInPipe = 0;
unsigned int pipePeeks=0;
while( (bytesInPipe==0) && (pipePeeks < MAX_PIPE_PEEKS) )
{
bSuccess = PeekNamedPipe( g_hChildStd_OUT_Rd, NULL, 0, NULL,
&bytesInPipe, NULL );
if( !bSuccess ) return bSuccess; // Bail on critical failure
++pipePeeks;
}
if( bytesInPipe > 0 )
{
// Read the data written to the pipe (and implicitly clear it)
DWORD dwRead;
CHAR *pipeContents = new CHAR[ bytesInPipe ];
bSuccess = ReadFile( g_hChildStd_OUT_Rd, pipeContents,
bytesInPipe, &dwRead, NULL );
if( !bSuccess || dwRead == 0 ) return FALSE; // Bail on critical failure
// "Cheat" - eliminate garbage at the end of the pipe
if( pipeContents[ bytesInPipe ] != '\0' )
pipeContents[ bytesInPipe ] = '\0';
}
UPDATE:
After further testing, I found that this is not quite reliable (shocking, huh?). I think I'm on the right track though for a relatively simple solution. Any ideas for getting this quick patch to work?

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