Redirecting CreateProcess input stream to a file - c++

Question

I'm using CreateProcess to substitute a system() call in my code. I was using:
system(xfoil.exe < create_results.txt");
Which I am substituing by this:
PROCESS_INFORMATION ProcessInfo; //This is what we get as an [out] parameter
STARTUPINFO StartupInfo; //This is an [in] parameter
LPCWSTR input_file = _tcsdup(TEXT(".\\create_results.txt"));
HANDLE inpfl = CreateFile(input_file, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
StartupInfo.hStdInput = inpfl;
ZeroMemory(&StartupInfo, sizeof(StartupInfo));
StartupInfo.cb = sizeof StartupInfo; //Only compulsory field
LPCWSTR exe_path =_tcsdup(TEXT(".\\xfoil.exe"));
if (CreateProcess(exe_path, NULL,
NULL, NULL, FALSE, CREATE_NEW_CONSOLE, NULL,
NULL, &StartupInfo, &ProcessInfo))
{
WaitForSingleObject(&ProcessInfo.hProcess, 2000);
CloseHandle(ProcessInfo.hThread);
CloseHandle(ProcessInfo.hProcess);
CloseHandle(inpfl);
}
else
{
CloseHandle(inpfl);
std::cout << "Could not create xfoil process" << std::endl;
}
The reason being I need to control how long the process is allowed to run ( 2000ms in this case), however it seems that this method does not work.
I'm redirecting the input of the process to the handle of the file I want as input (to substitute the < operator), but the process is not receiving anything. It does launch the xfoil.exe in a separate console, though.

Answer 1

You need to set file security attributes to allow handle to be inherited and startup info flag to make child process use the handle passed:
::STARTUPINFO startup_information{};
::SECURITY_ATTRIBUTES security_attributes
{
sizeof(::SECURITY_ATTRIBUTES)
, nullptr
, TRUE // allow handle to be inherited
};
::HANDLE const inpfl{::CreateFileW(input_file, GENERIC_READ, FILE_SHARE_READ, ::std::addressof(security_attributes), OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL)};
if(INVALID_HANDLE_VALUE == inpfl)
{
auto const last_error{::GetLastError()};
// handle error...
}
startup_information.cb = sizeof(startup_information);
startup_information.dwFlags = STARTF_USESTDHANDLES;
startup_information.hStdInput = inpfl;

Answer 2

PROCESS_INFORMATION ProcessInfo; //This is what we get as an [out] parameter
STARTUPINFO StartupInfo; //This is an [in] parameter
LPCWSTR input_file = _tcsdup(TEXT(".\\create_results.txt"));
HANDLE inpfl = CreateFile(input_file, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
StartupInfo.hStdInput = inpfl;
What happens to StartupInfo.hStdInput after the next call?
ZeroMemory(&StartupInfo, sizeof(StartupInfo));
Oops... hStdInput zeroed now
Doing this initially...
PROCESS_INFORMATION ProcessInfo = {};
STARTUPINFO StartupInfo = {};
... will prevent you from needing to zero anything... see
Also, according to CreateProcess StartupInfo documentation, you have to, for hStdInput, set dwFlags to STARTF_USESTDHANDLES, else the default input is the keyboard buffer