How to read output from cmd.exe using CreateProcess() and CreatePipe()
I have been trying to create a child process executing cmd.exe with a command-line designating /K dir. The purpose is to read the output from the command back into the parent process using pipes.
I've already got CreateProcess() working, however the step involving pipes are causing me trouble. Using pipes, the new console window is not displaying (like it was before), and the parent process is stuck in the call to ReadFile().
Does anyone have an idea of what I'm doing wrong?
#include <Windows.h>
#include <stdio.h>
#include <tchar.h>
#define BUFFSZ 4096
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;
int wmain(int argc, wchar_t* argv[])
{
int result;
wchar_t aCmd[BUFFSZ] = TEXT("/K dir"); // CMD /?
STARTUPINFO si;
PROCESS_INFORMATION pi;
SECURITY_ATTRIBUTES sa;
printf("Starting...\n");
ZeroMemory(&si, sizeof(STARTUPINFO));
ZeroMemory(&pi, sizeof(PROCESS_INFORMATION));
ZeroMemory(&sa, sizeof(SECURITY_ATTRIBUTES));
// Create one-way pipe for child process STDOUT
if (!CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &sa, 0)) {
printf("CreatePipe() error: %ld\n", GetLastError());
}
// Ensure read handle to pipe for STDOUT is not inherited
if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0)) {
printf("SetHandleInformation() error: %ld\n", GetLastError());
}
// Create one-way pipe for child process STDIN
if (!CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &sa, 0)) {
printf("CreatePipe() error: %ld\n", GetLastError());
}
// Ensure write handle to pipe for STDIN is not inherited
if (!SetHandleInformation(g_hChildStd_IN_Rd, HANDLE_FLAG_INHERIT, 0)) {
printf("SetHandleInformation() error: %ld\n", GetLastError());
}
si.cb = sizeof(STARTUPINFO);
si.hStdError = g_hChildStd_OUT_Wr;
si.hStdOutput = g_hChildStd_OUT_Wr;
si.hStdInput = g_hChildStd_IN_Rd;
si.dwFlags |= STARTF_USESTDHANDLES;
sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.lpSecurityDescriptor = NULL;
// Pipe handles are inherited
sa.bInheritHandle = true;
// Creates a child process
result = CreateProcess(
TEXT("C:\\Windows\\System32\\cmd.exe"), // Module
aCmd, // Command-line
NULL, // Process security attributes
NULL, // Primary thread security attributes
true, // Handles are inherited
CREATE_NEW_CONSOLE, // Creation flags
NULL, // Environment (use parent)
NULL, // Current directory (use parent)
&si, // STARTUPINFO pointer
&pi // PROCESS_INFORMATION pointer
);
if (result) {
printf("Child process has been created...\n");
}
else {
printf("Child process could not be created\n");
}
bool bStatus;
CHAR aBuf[BUFFSZ + 1];
DWORD dwRead;
DWORD dwWrite;
// GetStdHandle(STD_OUTPUT_HANDLE)
while (true) {
bStatus = ReadFile(g_hChildStd_OUT_Rd, aBuf, sizeof(aBuf), &dwRead, NULL);
if (!bStatus || dwRead == 0) {
break;
}
aBuf[dwRead] = '\0';
printf("%s\n", aBuf);
}
// Wait until child process exits
WaitForSingleObject(pi.hProcess, INFINITE);
// Close process and thread handles
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
printf("Stopping...\n");
return 0;
}
