C++信号

 C++信号
C++中各个类之间通讯主要通过指针，得相互include来include去，依赖关系很是复杂头痛。一个简单的方法是用信号来进行通讯：可以在发出信号的类中定义和发出信号，可以设为私有，这样可以防止其他类发出这种信号，而在被调用的类中定义被调用函数。初始化之后再链接信号和被调用函数。如以下使用了sigc++的例子(此例子来自gtkmm development team，以GNU General Public License version 2发布)；
//server.h
#include <sigc++/sigc++.h>

class Server
{
public:
  Server();
  virtual ~Server();

  virtual void do_something();

  //signal accessor:
  typedef sigc::signal<void, bool, int> type_signal_something;
  type_signal_something signal_something();

protected:
  type_signal_something m_signal_something;
};

//server.cc
#include "server.h"
#include <iostream>

Server::Server()
{
}

Server::~Server()
{
}

Server::type_signal_something Server::signal_something()
{
  return m_signal_something;
}

void Server::do_something()
{
  m_signal_something.emit(false, 5);
}

//client.h
#include <sigc++/sigc++.h>

//Client must inherit from sigc::trackable.
//because libsigc++ needs to keep track of the lifetime of signal handlers.
class Client : public sigc::trackable
{
public:
  Client();
  virtual ~Client();

  //Signal handler:
  virtual void on_server_something(bool a, int b);
};

//client.cc
#include "client.h"
#include <iostream>

Client::Client()
{
}

Client::~Client()
{
}

void Client::on_server_something(bool a, int b)
{
  std::cout << "Client::on_server_something() called with these parameters: "
      << a << ", " << b << std::endl;
}