Hello I am trying to make a front end GUI for cmd.exe so I can make it wider but I got stuck.
I try to design an API like this
char* Directory = WriteCommand("dir");
printf("- %s\n", Directory);
and the output look exactly like it would in a cmd window, except I have it in a string, so it would be
DATE TIME FILESIZE FILENAME
etc etc etc
and then I can issue
char* Up = WriteCommand ("cd ..");
and it will give me the above directory listing. So I want a terminal control through using pipes to read and write.
I have tried many things based on this MSDN sample code - https://msdn.microsoft.com/en-us/library/ms682499.aspx
But I think this code is only good to issue one command, and read one response, because right after it deadlocks as described here - https://blogs.msdn.microsoft.com/oldnewthing/20110707-00/?p=10223
I see several other questions here, like this one with similar problems - How to read output from cmd.exe using CreateProcess() and CreatePipe() but no solutions posted work for me.
So here is my code.
#include <windows.h>
#include <tchar.h>
#include <stdio.h>
#include <strsafe.h>
#define BUFSIZE 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;
HANDLE g_hInputFile = NULL;
void CreateChildProcess(void);
void WriteToPipe(char* Arg1);
void ReadFromPipe(void);
void ErrorExit(PTSTR);
int _tmain(int argc, TCHAR *argv[])
{
SECURITY_ATTRIBUTES saAttr;
printf("\n->Start of parent execution.\n");
// Set the bInheritHandle flag so pipe handles are inherited.
saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
saAttr.bInheritHandle = TRUE;
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe for the child process's STDOUT.
if (!CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0))
ErrorExit(TEXT("StdoutRd CreatePipe"));
// Ensure the read handle to the pipe for STDOUT is not inherited.
if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0))
ErrorExit(TEXT("Stdout SetHandleInformation"));
// Create a pipe for the child process's STDIN.
if (!CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0))
ErrorExit(TEXT("Stdin CreatePipe"));
// Ensure the write handle to the pipe for STDIN is not inherited.
if (!SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0))
ErrorExit(TEXT("Stdin SetHandleInformation"));
// Create the child process.
CreateChildProcess();
// Get a handle to an input file for the parent.
// This example assumes a plain text file and uses string output to verify data flow.
/*if (argc == 1)
ErrorExit(TEXT("Please specify an input file.\n"));
g_hInputFile = CreateFile(
argv[1],
GENERIC_READ,
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_READONLY,
NULL);
if (g_hInputFile == INVALID_HANDLE_VALUE)
ErrorExit(TEXT("CreateFile"));*/
// Write to the pipe that is the standard input for a child process.
// Data is written to the pipe's buffers, so it is not necessary to wait
// until the child process is running before writing data.
// Read from pipe that is the standard output for child process.
ReadFromPipe();
WriteToPipe("ipconfig");
// THIS IS WHERE DEADLOCK OCCURS, FROM HERE
// PROGRAM BECOMES UNRESPONSIVE - HOW TO FIX THIS?
ReadFromPipe();
printf("\n->End of parent execution.\n");
// The remaining open handles are cleaned up when this process terminates.
// To avoid resource leaks in a larger application, close handles explicitly.
return 0;
}
void CreateChildProcess()
// Create a child process that uses the previously created pipes for STDIN and STDOUT.
{
TCHAR szCmdline[] = TEXT("cmd.exe /k");
PROCESS_INFORMATION piProcInfo;
STARTUPINFO siStartInfo;
BOOL bSuccess = FALSE;
// Set up members of the PROCESS_INFORMATION structure.
ZeroMemory(&piProcInfo, sizeof(PROCESS_INFORMATION));
// Set up members of the STARTUPINFO structure.
// This structure specifies the STDIN and STDOUT handles for redirection.
ZeroMemory(&siStartInfo, sizeof(STARTUPINFO));
siStartInfo.cb = sizeof(STARTUPINFO);
siStartInfo.hStdError = g_hChildStd_OUT_Wr;
siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
siStartInfo.hStdInput = g_hChildStd_IN_Rd;
siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
// Create the child process.
bSuccess = CreateProcess(NULL,
"cmd.exe", // command line
NULL, // process security attributes
NULL, // primary thread security attributes
TRUE, // handles are inherited
0, // creation flags
NULL, // use parent's environment
NULL, // use parent's current directory
&siStartInfo, // STARTUPINFO pointer
&piProcInfo); // receives PROCESS_INFORMATION
// If an error occurs, exit the application.
if (!bSuccess)
ErrorExit(TEXT("CreateProcess"));
else
{
// Close handles to the child process and its primary thread.
// Some applications might keep these handles to monitor the status
// of the child process, for example.
CloseHandle(piProcInfo.hProcess);
CloseHandle(piProcInfo.hThread);
}
}
void WriteToPipe(char* Command)
// Read from a file and write its contents to the pipe for the child's STDIN.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
bSuccess = WriteFile(g_hChildStd_IN_Wr, Command, strlen(Command), &dwWritten, NULL);
if (bSuccess == FALSE)
printf("write fail\n");
printf("written = %i\n", dwWritten);
//for (;;)
//{
//bSuccess = ReadFile(g_hInputFile, chBuf, BUFSIZE, &dwRead, NULL);
//if (!bSuccess || dwRead == 0) break;
//bSuccess = WriteFile(g_hChildStd_IN_Wr, Command, strlen(Command), &dwWritten, NULL);
//if (bSuccess == FALSE)
//printf("write fail\n");
//printf("written = %i\n", dwWritten);
//}
// Close the pipe handle so the child process stops reading.
//if (!CloseHandle(g_hChildStd_IN_Wr))
//ErrorExit(TEXT("StdInWr CloseHandle"));
}
void ReadFromPipe(void)
// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
int i;
for (i = 0; i < 4; i++)
{
/*DWORD dwAvail = 0;
if (!PeekNamedPipe(g_hChildStd_OUT_Rd, NULL, 0, NULL, &dwAvail, NULL)) {
// error, the child process might have ended
break;
}
if (!dwAvail) {
// no data available in the pipe
break;
}*/
bSuccess = ReadFile(g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
if (!bSuccess || dwRead == 0) break;
/*bSuccess = WriteFile(hParentStdOut, chBuf, dwRead, &dwWritten, NULL);
if (!bSuccess) break;*/
chBuf[dwRead] = '\0';
printf("%i - %s\n", i, chBuf);
}
printf("done\n");
}
I issue the initial "cmd.exe" command which gives me the start of the command prompt. I now want to issue "ipconfig" (or any other command) to get networking info. The program deadlocks and becomes unresponsive. I can no longer read output of child process. How can I fix this? Thanks for your help.
