简单Trace类实现

　　《C++沉思录》27章内容修改后所得：

 /************************************************************************/
 /* Trace类，以及trace类输出重定向，C++沉思录27章                  */
 /************************************************************************/
 #pragma once
 #include <iostream>
 using namespace std;

 //打开/关闭trace输入输出流
 static const int trace_debug = ;

 //输出流
 class Channel
 {
 public:
     Channel (ostream* o = &std::cout): trace_file(o){}
     //重定向输出流
     void Reset(ostream* o = &std::cout)
     {
         trace_file = o;
     }
 private:
     friend class Trace;
     template<class T> friend class Obj_trace;
     ostream* trace_file;
 };
 typedef CSingleton<Channel> TraceChannel;    

 class Trace
 {
 public:
     Trace(const char* s,Channel* c = TraceChannel::Instance())
     {
         if (trace_debug)
         {
             name = s;
             cp = c;;
             if (cp && cp->trace_file)
             {
                 *cp->trace_file << "Trace begin : " << name << endl;
             }
         }
     }
     ~Trace()
     {
         if (trace_debug)
         {
             if (cp && cp->trace_file)
             {
                 *cp->trace_file << "Trace end : " << name <<endl;
             }
         }
     }
 private:
     Channel* cp;
     const char* name;
 };

 //传递类名给Obj_trace，可以作为待跟踪类的基类或成员变量存在
 template<class T>
 class Obj_trace
 {
 public:
     Obj_trace(Channel* c = TraceChannel::Instance()) : ct(++count)
     {
         if (trace_debug)
         {
             cp = c;
             if (cp && cp->trace_file)
             {
                 *cp->trace_file << "Trace obj begin : " << typeid(T).name() << " "<< ct << " constructed" << endl;
             }
         }
     }
     ~Obj_trace()
     {
         if (trace_debug)
         {
             if (cp && cp->trace_file)
             {
                 *cp->trace_file << "Trace obj end : " << typeid(T).name() << " "<< ct << " destoryed" << endl;
             }
         }
     }
 private:
     Channel* cp;
     const char* name;
     static int count;
     int ct;
 };

 //每个不同的type类型都有唯一对应的count
 template<class T>
 int Obj_trace<T>::count = ;