How to fully control a program within another program
 

I am working on a program, called A, that should run another program, called B. I'm using "fork() " and "execvp()" together to run the program B. That's all fine but the problem is that the program B is asking for a password after it has been executed. How can program A place a password onto to the stdio, or something, after it has executed the program B in order to keep it running.
Regards

i think , but not shure , that it should be done with redirecting standard output and standard input from process

Try opening the program B stdin (coz almost B expect the password from stdin).

consider using pipes for nicer IPC(InterProcess Communication: look at the popen function manual)

one last note: some programs do a check to look if they are running on terminal or not.

thanks, it works fine for me using popen(). But when writing to the pipe, using fprintf(), I am always getting this error/warning when running the program:
stty: standard input: Invalid argument

The program works fine, but I would like to get rid of this message.
regards

http://www.advancedlinuxprogramming.com

That all you need to learn how to communicate between process. The tutorial is quite in depth.

The message is printed by the program you call, so you cannot direct supress it (except by supressing the output stream it is printed on which is probably a bad idea).

the correct way to do this would be to create a virtual tty for the child to run in. You can do that directly in C, or you can use `expect` or a similar tty wrapper.