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 Gtk::Main::input.connect(const SlotType& sd, int source, GdkInputCondition 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 (and somewhat dirty) example follows. To use the example just execute it from a terminal; it doesn't create a window. It will create a pipe named testpipe in the current directory. Then start another shell and execute cat >testpipe. The example will print each line you enter until you type quit.
Source location: examples/input/input.cc
#include <gtkmm/main.h> #include <fcntl.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fstream> #include <iostream> #include <memory> using std::istream; using std::auto_ptr; auto_ptr<istream> input; // this will be our signal handler for read operations // there is not much to say. just read a string, // print it and quit the application if the string was quit void MyCallback(int, GdkInputCondition) { Gtk::string dummy; do { (*input) >> dummy; cout << dummy << endl; if(dummy == "quit") Gtk::Main::quit(); } while(input->fail()); } int main (int argc, char *argv[]) { // the usual Gtk::Main object Gtk::Main app(argc, argv); // create a fifo for testing purposes if (mkfifo("testfifo",0666) != 0) { cerr << "error creating fifo" << endl; return -1; } // open the fifo input=new ifstream("testfifo"); // int fd = open("testfifo", 0); // if (fd == -1) { // cerr << "error opening fifo" << endl; // return -1; // } // assign the fifo's filedescriptor to our ifstream object //This sucks; it will only ever work with libstdc++-v3, as // both istream::__filebuf_type and the basic_filebuf contructor // that takes an fd are libstdc++-v3 specific. //input=new istream(new ifstream::__filebuf_type(fd,"testfifo")); // connect the signal handler app.input.connect(sigc::ptr_fun(MyCallback), fd, GDK_INPUT_READ); // and last but not least - run the application main loop app.run(); // now remove the temporary fifo if(unlink("testfifo")) cerr << "error removing fifo" << endl; return 0; }