Introduction

+ + + libsigc++ + + Ainsley + Pereira + + September 2002 + September 2002. Updated January 2004 by Murray Cumming + + libsigc++ is a C++ template library implementing typesafe callbacks. This is an intro to libsigc++. + + + + +Introduction + +

+Motivation There are many situations in which it is desirable to decouple code that detects an event, and the code that deals with it. This is especially common in @@ -69,14 +69,15 @@ register_click_handler(okbutton, clicked, somedata); For the other side of the fence, libsigc++ provides signals, to which the client can attach slots. When the signal is emitted, all the connected slots are called. - +

- -Connecting your code to signals + +Connecting your code to signals + +

+A simple example - -A simple example So to get some experience, lets look at a simple example... Lets say you and I are writing an application which informs the user when @@ -138,10 +139,10 @@ int main() ./example1 (Try not to panic when the aliens land!) - +

- -Using a member function +

+Using a member function Suppose you found a more sophisticated alien alerter class on the web, such as this: @@ -187,10 +188,10 @@ int main() With a lambda expression you would lose the automatic disconnection that the combination of sigc::trackable and sigc::mem_fun() offers. - +

- -Signals with parameters +

+Signals with parameters Functions taking no parameters and returning void are quite useful, especially when they're members of classes that can store unlimited amounts of @@ -252,10 +253,10 @@ int main() Easy. - +

- -Disconnecting +

+Disconnecting If you decide you no longer want your code to be called whenever a signal is emitted, you must remember the return value of connect(), which we've been @@ -263,14 +264,15 @@ int main() connect() returns a sigc::connection object, which has a disconnect() member method. This does just what you think it does. - +

- -Writing your own signals + +Writing your own signals + +

+Quick recap - -Quick recap If all you want to do is use gtkmm, and connect your functionality to its signals, you can probably stop reading here. @@ -315,10 +317,11 @@ void AlienDetector::run() // they landed in the carpark after all. } - +

+ +

+What about return values? - -What about return values? If you only ever have one slot connected to a signal, or if you only care about the return value of the last registered one, it's quite straightforward: @@ -328,14 +331,15 @@ int a_return_value; a_return_value = somesignal.emit(); - +

- -Advanced topics + +Advanced topics + +

+Rebinding - -Rebinding Suppose you already have a function that you want to be called when a signal is emitted, but it takes the wrong argument types. For example, lets try to attach the warn_people(std::string) function to the detected signal @@ -398,10 +402,11 @@ myaliendetector.signal_detected.connect( sigc::hide<std::string>( sigc::pt hide the first argument of 3, for example, only the last). sigc::hide_return effectively makes the return type void. - +

+ +

+Retyping - -Retyping A similar topic is retyping. Perhaps you have a signal that takes an int, but you want to connect a function that takes a double. @@ -420,11 +425,12 @@ asignal.connect( sigc::retype( sigc::ptr_fun(&dostuff) ) ); If you only want to change the return type, you can use sigc::retype_return(). retype_return() needs one template argument, the new return type. - +

- -Reference - See the reference documentation online + +Reference + + See the reference documentation online

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