Reserving stdiin for parent process - linux

Question

After several days of searching it's time to ask. Environment is Ubuntu 12.04/Gnome.
I'm developing some embedded code on the ubuntu box and testing as much as I can in that environment before porting over to the embedded processor. The current routine is a real time fast fourier transform and I want to use gnuplot to display the results. So I want my test code AND gnuplot to run in the foreground at the same time and communicate via a pipe.
I did the usual popen() call and that worked except for one thing. stdin for the child (gnuplot) is still attached to the console. It is in contention with the parent process. The parent process needs to receive keystrokes to modify its behaviour. Sometimes the parent gets the keystroke and sometimes gnuplot does.
So I've tried the fork/exec path. Specifically
pid_t pg = tcgetpgrp(1); // get process group associated with stdout
cerr << "pid_t pg = " << pg << endl;
cerr << "process pid is " << getpid() << endl;
if (pipe(pipefd) == -1) {// open the pipe
cerr << "pipe failure" << endl;
exit(3);
} // if pipe
cpid = fork();
if (cpid == -1) {
cerr << "fork failure" << endl;
exit(1);
}
if (cpid == 0) { // this is the child process
if (tcsetpgrp(1, pg) == -1) { // this should set the process associated with stdin (gnuplot) with the
cerr << "tcsetgrp failed" << endl; // foreground terminal.
exit(7);
}
close(pipefd[1]); // close child's writing handle
if (pipefd[0] != STDIN_FILENO) { // this changes the file descripter of stdin back to 0
if ( dup2(pipefd[0], STDIN_FILENO) != STDIN_FILENO) {
cerr << "dup2 error on stdin" << endl;
exit(6);
}
}
if (execl("/usr/bin/gnuplot", "gnuplot", "-background", "white", "-raise", (char *) NULL)) {
cerr << "execl failed" << endl;
exit(2);
} else // if exec
close(pipefd[0]); // close parent's reading handle
} // if cpid
// back in parent process
This fires off gnuplot as I expect it should. I can see gnuplot consuming all the resources of one core as it normally does. The problem is that no graph appears on the screen.
So my question is, how do I start a child process, totally detach it from the console so it won't get any keystrokes and get the output of gnuplot to display?