// Execute a command and get the results in a CString.
// Synchronously launches a child process and waits up to 2 seconds for completion.
// Uses a pipe to get the output of the child process.
// Does not pipe to stdin of child process.
// Example usage:
//   CString str;
//   str = ExecCmd( "ping 127.0.0.1 -n 99 " );  // This ping command will be terminated early before the -n 99 completes.
//   str.Replace( "\x0d\x0d\x0a", "\x0d\x0a" ); // fixes some ugly non-standard line terminators created by ping.
//
//   str = ExecCmd( "java -version" ); // A more practical usage.
//
CString ExecCmd( LPCSTR pCmdArg)
{
   // Handle Inheritance - to pipe child's stdout via pipes to parent, handles must be inherited.
   //   SECURITY_ATTRIBUTES.bInheritHandle must be TRUE
   //   CreateProcess parameter bInheritHandles must be TRUE;
   //   STARTUPINFO.dwFlags must have STARTF_USESTDHANDLES set.
 
   CString strResult; // Contains result of cmdArg.
 
   HANDLE hChildStdoutRd; // Read-side, used in calls to ReadFile() to get child's stdout output.
   HANDLE hChildStdoutWr; // Write-side, given to child process using si struct.
 
   BOOL fSuccess;
 
   // Create security attributes to create pipe.
   SECURITY_ATTRIBUTES saAttr = {sizeof(SECURITY_ATTRIBUTES)} ;
   saAttr.bInheritHandle       = TRUE; // Set the bInheritHandle flag so pipe handles are inherited by child process. Required.
   saAttr.lpSecurityDescriptor = NULL;
 
   // Create a pipe to get results from child's stdout.
   // I'll create only 1 because I don't need to pipe to the child's stdin.
   if ( !CreatePipe(&hChildStdoutRd, &hChildStdoutWr, &saAttr, 0) )
   {
      return strResult;
   }
 
   STARTUPINFO si = { sizeof(STARTUPINFO) }; // specifies startup parameters for child process.
 
   si.dwFlags     = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES; // STARTF_USESTDHANDLES is Required.
   si.hStdOutput  = hChildStdoutWr; // Requires STARTF_USESTDHANDLES in dwFlags.
   si.hStdError   = hChildStdoutWr; // Requires STARTF_USESTDHANDLES in dwFlags.
   // si.hStdInput remains null.
   si.wShowWindow = SW_HIDE; // Prevents cmd window from flashing. Requires STARTF_USESHOWWINDOW in dwFlags.
 
   PROCESS_INFORMATION pi  = { 0 };
 
   // Create the child process.
   fSuccess = CreateProcess(
      NULL,
      (LPSTR)pCmdArg,     // command line
      NULL,               // process security attributes
      NULL,               // primary thread security attributes
      TRUE,               // TRUE=handles are inherited. Required.
      CREATE_NEW_CONSOLE, // creation flags
      NULL,               // use parent's environment
      NULL,               // use parent's current directory
      &si,                // __in, STARTUPINFO pointer
      &pi);               // __out, receives PROCESS_INFORMATION
 
   if (! fSuccess)
   {
      return strResult;
   }
 
   // Wait until child processes exit. Don't wait forever.
   WaitForSingleObject( pi.hProcess, 2000 );
   TerminateProcess( pi.hProcess, 0 ); // Kill process if it is still running. Tested using cmd "ping blah -n 99"
 
   // Close the write end of the pipe before reading from the read end of the pipe.
   if (!CloseHandle(hChildStdoutWr))
   {
      return strResult;
   }
 
   // Read output from the child process.
   for (;;)
   {
      DWORD dwRead;
      CHAR chBuf[4096];
 
      // Read from pipe that is the standard output for child process.
      bool done = !ReadFile( hChildStdoutRd, chBuf, 4096, &dwRead, NULL) || dwRead == 0;
      if( done )
      {
         break;
      }
 
      // Append result to string.
      strResult += CString( chBuf, dwRead) ;
   }
 
   // Close process and thread handles.
   CloseHandle( hChildStdoutRd );
 
   // CreateProcess docs specify that these must be closed. 
   CloseHandle( pi.hProcess );
   CloseHandle( pi.hThread );
 
   return strResult;
}