How to read output from cmd.exe using CreateProcess() and CreatePipe()

Question

How to read output from cmd.exe using CreateProcess() and CreatePipe()

I have been trying to create a child process executing c

Answer 1

I too have same scenario. in my case from Lib, need to execute internal exe and read output. The following works without any issues.

  void executeCMDInNewProcessAndReadOutput(LPSTR lpCommandLine)
    {
        STARTUPINFO si;
        SECURITY_ATTRIBUTES sa;
        PROCESS_INFORMATION pi;
        HANDLE g_hChildStd_IN_Rd, g_hChildStd_OUT_Wr, g_hChildStd_OUT_Rd, g_hChildStd_IN_Wr;  //pipe handles
        char buf[1024];           //i/o buffer

        sa.nLength = sizeof(SECURITY_ATTRIBUTES);
        sa.bInheritHandle = TRUE;
        sa.lpSecurityDescriptor = NULL;

        if (CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &sa, 0))   //create stdin pipe
        {
            if (CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &sa, 0))  //create stdout pipe
            {

                //set startupinfo for the spawned process
                /*The dwFlags member tells CreateProcess how to make the process.
                STARTF_USESTDHANDLES: validates the hStd* members.
                STARTF_USESHOWWINDOW: validates the wShowWindow member*/
                GetStartupInfo(&si);

                si.dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW;
                si.wShowWindow = SW_HIDE;
                //set the new handles for the child process
                si.hStdOutput = g_hChildStd_OUT_Wr;
                si.hStdError = g_hChildStd_OUT_Wr;
                si.hStdInput = g_hChildStd_IN_Rd;

                //spawn the child process
                if (CreateProcess(NULL, lpCommandLine, NULL, NULL, TRUE, CREATE_NEW_CONSOLE,
                    NULL, NULL, &si, &pi))
                {
                    unsigned long bread;   //bytes read
                    unsigned long avail;   //bytes available
                    memset(buf, 0, sizeof(buf));

                    for (;;)
                    {
                        PeekNamedPipe(g_hChildStd_OUT_Rd, buf, 1023, &bread, &avail, NULL);
                        //check to see if there is any data to read from stdout
                        if (bread != 0)
                        {
                            if (ReadFile(g_hChildStd_OUT_Rd, buf, 1023, &bread, NULL))
                            {
                                break;
                            }
                        }
                    }

                    //clean up all handles
                    CloseHandle(pi.hThread);
                    CloseHandle(pi.hProcess);
                    CloseHandle(g_hChildStd_IN_Rd);
                    CloseHandle(g_hChildStd_OUT_Wr);
                    CloseHandle(g_hChildStd_OUT_Rd);
                    CloseHandle(g_hChildStd_IN_Wr);
                }
                else
                {
                    CloseHandle(g_hChildStd_IN_Rd);
                    CloseHandle(g_hChildStd_OUT_Wr);
                    CloseHandle(g_hChildStd_OUT_Rd);
                    CloseHandle(g_hChildStd_IN_Wr);
                }
            }
            else
            {
                CloseHandle(g_hChildStd_IN_Rd);
                CloseHandle(g_hChildStd_IN_Wr);
            }
        }
    }