boost库学习笔记 代码示例1 boost::function

/*
 * function.cpp
 *
 * Created on: 2013-7-22
 * Author: root
 */
/*
#include <iostream>
#include "boost/function.hpp"

bool some_func(int i,double d)
{
    return i > d;
}

int main()
{
    boost::function<bool (int,double)>f;
    f = &some_func;

    f(10,1.1);
}
*/

#include <iostream>
#include <vector>
#include <algorithm>
#include "boost/function.hpp"

void print_new_value(int i) {
    std::cout << "The value has been updated and is now " << i << '\n';
}

void interested_in_the_change(int i) {
    std::cout << "Ah,the value has changed."<< i << "\n";
}

//class notifier {
//    typedef void (*function_type)(int);
//    std::vector<function_type> vec_;
//    int value_;
//public:
//    void add_observer(function_type t) {
//        vec_.push_back(t);
//    }
//
//    void change_value(int i){
//        value_ = i;
//        for(std::size_t i=0; i<vec_.size(); ++i) {
//            (*vec_[i])(value_);
//        }
//    }
//};
//改进后的类，支持对象，指针,boost::function实例
class notifier {
    typedef boost::function<void (int)>function_type;
    std::vector<function_type> vec_;
    int value_;
public:
    template <typename T> void add_observer(T t) {
        vec_.push_back(function_type(t));
    }

    void change_value(int i){
        value_ = i;
        for(std::size_t i=0; i<vec_.size(); ++i) {
            vec_[i](value_);
        }
    }
};

class knows_the_previous_value{
    int last_value_;
public:
    void operator()(int i) {
        static bool first_time = true;
        if(first_time) {
            last_value_ = i;
            std::cout << "This is the first change of value, \
            so I don't know the previous one.\n";
            first_time = false;
            return;
        }
        std::cout << "Previous value was " << last_value_ << '\n';
        last_value_ = i;
    }
};
/*
int main() {
    notifier n;
    n.add_observer(&print_new_value);
    n.add_observer(&interested_in_the_change);
    n.add_observer(knows_the_previous_value()); //使用带状态（参数）的对象是这个功能的亮点

    n.change_value(42);
    std::cout << "\n";
    n.change_value(30);
}
*/