boost—— 函数与回调ref小工具类

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重点内容

#if 0namespace boost {  template<typename T> class reference_wrapper;  reference_wrapper<T> ref(T&);  reference_wrapper<T const> cref(T const&);  unwrap_reference<T>::type& unwrap_ref(T&);  template<typename T> class is_reference_wrapper;  template<typename T> class unwrap_reference;}reference_wrapper摘要：template<typename T> class reference_wrapper {public:  // types  typedef T type;  // construct/copy/destruct  explicit reference_wrapper(T&);  // access  operator T&() const;  T& get() const;  T* get_pointer() const;private:    T*t;};// constructorsreference_wrapper<T> ref(T&);reference_wrapper<T const> cref(T const&);// accessunwrap_reference<T>::type& unwrap_ref(T&);/*reference_wrapper支持拷贝构造和赋值，而引用类型是不可赋值的*/#endif

#include <iostream>#include <string>#include <vector>#include <set>#include <map>#include <algorithm>#include <boost/ref.hpp>#include <boost/assign.hpp>#include <math.h>#include <typeinfo>#include <boost/typeof/typeof.hpp>using namespace boost;using namespace std;int main( int argc,char **argv){    int x = 20;    reference_wrapper<int> rw(x);   //包装类型的引用    assert(x = rw);     //隐式转换为int类型    (int &)rw = 1000;   //显示转换为int&类型，用于左值    assert(1000 == x);    reference_wrapper<int> rw2(rw); //拷贝构造    assert(1000 == rw2.get());    string str;    reference_wrapper<string> rws(str); //包装字符串的引用    *rws.get_pointer() = "hello world"; //指针操作    cout << rws.get().size() << endl;       /*这里的get函数先获得被包装的真正的对象，然后调用其方法。如果和下面一样，则会引发编译错误    cout << rws.size() << endl*/    /*reference_wrapper的两个工厂函数*/    double x1 = 2.4448;    BOOST_AUTO(rw3,cref(x));    //包装double const    cout << typeid(rw3).name() << endl;    string str1;    BOOST_AUTO(rws2,ref(str1)); //包装字符串    cout << typeid(rws2).name() << endl;    cout << sqrt(cref(x1)) << endl; //直接利用其的拷贝，然后直接计算    /*操作包装的两个类*/    vector<int> iv(10,3);    assert(is_reference_wrapper<BOOST_TYPEOF(cref(iv))>::value);    //经过包装    assert(!is_reference_wrapper<BOOST_TYPEOF(iv)>::value); //未经包装    string str2;    /*is_reference_wrapper的bool成员变量value可以判断其是否经过包装     * unwrap_reference无论是否经过包装，都可以通过内部类型确定T的真实类型*/    cout << typeid(unwrap_reference<BOOST_TYPEOF(ref(str))>::type).name() << endl;    cout << typeid(unwrap_reference<BOOST_TYPEOF(str2)>::type).name() << endl;     /*unwrap_ref解开包装，返回被包装对象的引用*/    set<double> sd;    BOOST_AUTO(rw5,ref(sd));    //获得一个包装    unwrap_ref(rw5).insert(13.98);  //解包并插入对象    string str12("hello world");    BOOST_AUTO(rws12,cref(str12));    cout << unwrap_ref(rws) << endl;    //解包    cout << unwrap_ref(str12) << endl;  //对未包装对象解包     return (0);}

ref的使用实例，包装引用

#include <iostream>#include <string>#include <vector>#include <set>#include <map>#include <algorithm>#include <boost/ref.hpp>#include <boost/assign.hpp>#include <math.h>#include <typeinfo>#include <boost/typeof/typeof.hpp>using namespace boost;using namespace std;class big_class{private:    int x;public:    big_class():x(0){    }    void print()    {        cout << "big_class" << ++x << endl;    }       };template<typename T>void print(T a){    for(int i = 0;i < 2;++i){        unwrap_ref(a).print();    }}int main(int argc,char **argv){    big_class c;    BOOST_AUTO(rw,ref(c));    c.print();    print(c);    print(rw);    print(c);    c.print();     return (0);}

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