<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Monitoring I/O</title> <link rel="stylesheet" href="style.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2"> <link rel="start" href="index.html" title="Programming with gtkmm"> <link rel="up" href="ch21.html" title="Chapter 21. Timeouts, I/O and Idle Functions"> <link rel="prev" href="ch21.html" title="Chapter 21. Timeouts, I/O and Idle Functions"> <link rel="next" href="ch21s03.html" title="Idle Functions"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr><th colspan="3" align="center">Monitoring I/O</th></tr> <tr> <td width="20%" align="left"> <a accesskey="p" href="ch21.html"><img src="../icons/prev.png" alt="Prev"></a> </td> <th width="60%" align="center">Chapter 21. Timeouts, I/O and Idle Functions </th> <td width="20%" align="right"> <a accesskey="n" href="ch21s03.html"><img src="../icons/next.png" alt="Next"></a> </td> </tr> </table> <hr> </div> <div class="sect1" lang="en"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="sec-monitoring_io"></a>Monitoring I/O</h2></div></div></div> <p> TODO: This is now in Glib, not Gdk. A nifty feature of GDK (one of the libraries underlying <span class="application">gtkmm</span>) 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: </p> <p> </p> <pre class="programlisting"> sigc::connection Glib::Main::SignalInput::connect(const SlotType& sd, int source, Glib::InputCondition condition); </pre> <p> </p> <p> The first argument is a slot (<code class="classname">SlotType</code> is a typedef to a <code class="classname">sigc::slot<></code>) 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 <code class="literal">|</code>) of: </p> <div class="itemizedlist"><ul type="disc"> <li><p> GDK_INPUT_READ - Call your method when there is data ready for reading on your file descriptor. </p></li> <li><p> GDK_INPUT_WRITE - Call your method when the file descriptor is ready for writing. </p></li> <li><p> GDK_INPUT_EXCEPTION - Call your method when an exception happened on the file descriptor. </p></li> </ul></div> <p> The return value is a <code class="classname">sigc::connection</code> that may be used to stop monitoring this file descriptor using its <code class="function">disconnect()</code> method. The <em class="parameter"><code>sd</code></em> signal handler should be declared as follows: </p> <p> </p> <pre class="programlisting"> void input_callback(int source, GdkInputCondition condition); </pre> <p> </p> <p> where <em class="parameter"><code>source</code></em> and <em class="parameter"><code>condition</code></em> are as specified above. As usual the slot is created with <code class="function">sigc::mem_fun()</code> (for a member method of an object.), or <code class="function">sigc::ptr_fun()</code> (for a function). </p> <p> 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 <code class="literal">testfifo</code> in the current directory. Then start another shell and execute <code class="literal">echo "Hello" > testfifo</code>. The example will print each line you enter until you execute <code class="literal">echo "Q" > testfifo</code>. </p> <p><a class="ulink" href="../../../examples/book/input/" target="_top">Source Code</a></p> <p>File: <code class="filename">main.cc</code> </p> <pre class="programlisting"> #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; #ifdef GLIBMM_EXCEPTIONS_ENABLED iochannel->read_line(buf); #else std::auto_ptr<Glib::Error> ex; iochannel->read_line(buf, ex); if(ex.get()) std::cerr << "Error: " << ex->what() << std::endl; #endif //GLIBMM_EXCEPTIONS_ENABLED 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; } </pre> </div> <div class="navfooter"> <hr> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"> <a accesskey="p" href="ch21.html"><img src="../icons/prev.png" alt="Prev"></a> </td> <td width="20%" align="center"><a accesskey="u" href="ch21.html"><img src="../icons/up.png" alt="Up"></a></td> <td width="40%" align="right"> <a accesskey="n" href="ch21s03.html"><img src="../icons/next.png" alt="Next"></a> </td> </tr> <tr> <td width="40%" align="left" valign="top">Chapter 21. 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