> The main point I try to understand is how a gui library interacts > with unix system call and other system tools. If I develop a console > (CLI) based program, and later implement the same program in gui then > what I need to do. Rewrite it with C++ and fltk or develop a gui (with > buttons, labels, text boxes etc) and attach the native c program to > it.
Command line programs and GUIs usually work in completely different ways. The command line allows input and produces output based on it, and the code is usually very sequential in nature. GUIs tend to be event driven with internal state machines, because at any point there are so many different things that the user can do (hide/show/resize the window, click on different buttons, enter things in different fields, and you have very little control over what is going to happen next. So it's not always a straightforward task to add a GUI to a command line utility. Secondly, you need to understand that there are different ways of one program calling and interacting with another. In Unix, the system() call is probably the crudest: the thread of execution in your program is completely suspended while the called program is running. Of course, you may use fork() or threads, but your child process or thread will not get back full control until the system() call completes. To allow a bit more interaction between your program and the called one, you can use popen(), but your program still needs to handle asynchronous communication with the one it is calling. None of this is FLTK specific. If you are handling asynchronous communications in FLTK you are probably going to need a multithreaded application, where the main thread handles the GUI (some operating systems require this so this is the FLTK advice for portability reasons) and the other threads do the work. Then you can either arrange for the main GUI thread to read data from the other threads, or the other threads have to call a lock, request the GUI to do some update, and then unlock again, and then let the GUI thread do the update when it is next scheduled to do so. Greg's Cheat Sheet has several examples of popen: http://seriss.com/people/erco/fltk/#add_fd http://seriss.com/people/erco/fltk/#SimpleTerminal Locking is demonstrated in the fltk-1.3/test/threads.cxx demo. Hope this helps. D. _______________________________________________ fltk mailing list [email protected] http://lists.easysw.com/mailman/listinfo/fltk
