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 = 1;

//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 = 0;