fprintf not writing to the pipe

I am successfully opening the pipe i.e gnuplot window using _popen. But not able to write to the stream using fprintf. I have checked the file pointer value and it is not null. I searched many sources and used fflush and it is not working. I could not find a solution.

Actually I have asked a similar question before here gnuplot c++ interface through pipes -cannot open wgnuplot reposting with some modifications.

Any suggestions would be helpful..

FILE* gp;
   string command = "set style data lines\n" ;
   char *path = "\"C:\\Program Files\\gnuplot\\bin\\wgnuplot\" -persist";
 
   gp = _popen(path , "wt");
 
   if (gp == NULL)
     return -1;
 
  fprintf(gp,command );
  fflush(gp);
  _pclose(gp);
 

I used this code without using pipes and it uses createprocess. Here also the same situation,The gnuplot.exe opens but with no output plot.

int _tmain (int argc, LPTSTR argv [])
 
 {
     DWORD i;
     HANDLE hReadPipe, hWritePipe;
 
     SECURITY_ATTRIBUTES PipeSA = {sizeof (SECURITY_ATTRIBUTES), NULL, TRUE};
             /* Init for inheritable handles. */
     TCHAR outBuf[ ] = TEXT("a=2; plot sin(a*x)/x; pause mouse; plot exp(-a*x); pause mouse") ;  
     TCHAR inBuf[80];
     DWORD dwWritten, dwRead ;
     BOOL  bSuccess = FALSE;
     PROCESS_INFORMATION  ProcInfo2;
     STARTUPINFO StartInfoCh2;
 
 
     /* Startup info for the Gnuplot process. */
 
     GetStartupInfo (&StartInfoCh2);
 
     /* Create an anonymous pipe with default size.
         The handles are inheritable. */
 
     bSuccess = CreatePipe (&hReadPipe, &hWritePipe, &PipeSA, 0);
     if (bSuccess == TRUE) printf("pipe created\n");
 
     WriteFile(hWritePipe, outBuf, sizeof(outBuf), &dwWritten, NULL) ;   
     printf("Wrote %d bytes to Gnuplot\n", dwWritten) ;
 
     CloseHandle (hWritePipe);
 
     /* Repeat (symmetrically) for the child process. */
 
     StartInfoCh2.hStdInput  = hReadPipe;
     StartInfoCh2.hStdError  = GetStdHandle (STD_ERROR_HANDLE);
     StartInfoCh2.hStdOutput = GetStdHandle (STD_OUTPUT_HANDLE);
     StartInfoCh2.dwFlags = STARTF_USESTDHANDLES;
     bSuccess = FALSE ;
     bSuccess = CreateProcess ("C:\\Program Files\\gnuplot\\bin\\wgnuplot.exe", NULL, NULL, NULL,
             TRUE,0, NULL, NULL, &StartInfoCh2, &ProcInfo2);
     if (bSuccess == TRUE)
       printf("Created Gnuplot Process\n" ) ;
 
     WaitForSingleObject (ProcInfo2.hProcess, INFINITE);
     CloseHandle (ProcInfo2.hThread); 
     CloseHandle (hReadPipe);
 
     /* Wait for Gnuplot process to complete.*/
 
     CloseHandle (ProcInfo2.hProcess);
     return 0;
 }
 

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