TODO: This is now in Glib, not Gdk. A nifty feature of GDK (one of the libraries underlying gtkmm) is the ability to have it check for data on a file descriptor for you. This is especially useful for networking applications. The following method is used to do this:
sigc::connection Glib::Main::SignalInput::connect(const SlotType& sd, int source, Glib::InputCondition condition);
The first argument is a slot (SlotType is a typedef to a sigc::slot<>) you wish to have called when then the
specified event (see argument 3) occurs on the file descriptor you
specify using argument two. Argument three may be one or more
(using |
) of:
GDK_INPUT_READ - Call your method when there is data ready for reading on your file descriptor.
GDK_INPUT_WRITE - Call your method when the file descriptor is ready for writing.
GDK_INPUT_EXCEPTION - Call your method when an exception happened on the file descriptor.
The return value is a sigc::connection that may be used to stop monitoring
this file descriptor using its disconnect
method.
The sd
signal handler should be declared as follows:
void input_callback(int source, GdkInputCondition condition);
where source
and condition
are as specified above. As usual
the slot is created with sigc::mem_fun()
(for a member method of an object.), or sigc::ptr_fun
(for a function).
A little example follows. To use the example just execute it from a terminal;
it doesn't create a window. It will create a pipe named
testfifo
in the current directory. Then start another shell
and execute echo "Hello" > testfifo
. The example will
print each line you enter until you execute echo "Q" >
testfifo
.
File: main.cc
#include <gtkmm/main.h> #include "gtkmmconfig.h" //For HAVE_MKFIFO #include <fcntl.h> #include <iostream> #include <unistd.h> //The SUN Forte compiler puts F_OK here. //The SUN Forte compiler needs these for mkfifo: #include <sys/types.h> #include <sys/stat.h> int read_fd; Glib::RefPtr<Glib::IOChannel> iochannel; /* send to the fifo with: echo "Hello" > testfifo quit the program with: echo "Q" > testfifo */ // this will be our signal handler for read operations // it will print out the message sent to the fifo // and quit the program if the message was 'Q'. bool MyCallback(Glib::IOCondition io_condition) { if ((io_condition & Glib::IO_IN) == 0) { std::cerr << "Invalid fifo response" << std::endl; } else { Glib::ustring buf; iochannel->read_line (buf); std::cout << buf; if (buf == "Q\n") Gtk::Main::quit (); } return true; } int main(int argc, char *argv[]) { // the usual Gtk::Main object Gtk::Main app(argc, argv); if (access("testfifo", F_OK) == -1) { // fifo doesn't exit - create it #ifdef HAVE_MKFIFO if (mkfifo("testfifo", 0666) != 0) { std::cerr << "error creating fifo" << std::endl; return -1; } #else std::cerr << "error creating fifo: This platform does not have mkfifo()" << std::endl; #endif //HAVE_MKFIFO } read_fd = open("testfifo", O_RDONLY); if (read_fd == -1) { std::cerr << "error opening fifo" << std::endl; return -1; } // connect the signal handler Glib::signal_io().connect(sigc::ptr_fun(MyCallback), read_fd, Glib::IO_IN); // Creates a iochannel from the file descriptor iochannel = Glib::IOChannel::create_from_fd(read_fd); // and last but not least - run the application main loop app.run(); // now remove the temporary fifo if(unlink("testfifo")) std::cerr << "error removing fifo" << std::endl; return 0; }