转自:http://www.vimer.cn/2011/01/%E5%B7%A7%E7%94%A8%E5%AE%8F%E5%AE%9A%E4%B9%89%E6%9D%A5%E7%AE%80%E5%86%99%E4%BB%A3%E7%A0%81.html

通过设计模式的角度来说,就是模板方法,已经有一个基类,需要定义很多子类来实现其方法。
但是类名都只有一部分不同,且构造函数的入参也只有一部分不同。
如代码:

#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <map>
using namespace std;
class EMA
{
    public:
        EMA(string a,string b,string c,string d,string e)
        {
            cout <<a<<","<<b<<","<<c<<","<<d<<","<<e<<endl;
        }
};
class EMA4CGI_1ST:public EMA{
    public:
        EMA4CGI_1ST():EMA(
                "app_mng.1ST_EMA_AVG",
                "app_mng.1ST_EMA_HWM",
                "app_mng.1ST_EMA_TMO",
                "app_mng.1ST_EMA_N",
                "app_mng.1ST_EMA_RATIO"
                ){}
        ~EMA4CGI_1ST() {}
};
class EMA4CGI_2ND:public EMA{
    public:
        EMA4CGI_2ND():EMA(
                "app_mng.2ND_EMA_AVG",
                "app_mng.2ND_EMA_HWM",
                "app_mng.2ND_EMA_TMO",
                "app_mng.2ND_EMA_N",
                "app_mng.2ND_EMA_RATIO"
                ){}
        ~EMA4CGI_2ND() {}
};
class EMA4CGI_3RD:public EMA{
    public:
        EMA4CGI_3RD():EMA(
                "app_mng.3RD_EMA_AVG",
                "app_mng.3RD_EMA_HWM",
                "app_mng.3RD_EMA_TMO",
                "app_mng.3RD_EMA_N",
                "app_mng.3RD_EMA_RATIO"
                ){}
        ~EMA4CGI_3RD() {}
};
int main(int argc, const char *argv[])
{
    EMA4CGI_1ST();
    EMA4CGI_2ND();
    EMA4CGI_3RD();
    return 0;
}

输出如下:

app_mng.1ST_EMA_AVG,app_mng.1ST_EMA_HWM,app_mng.1ST_EMA_TMO,app_mng.1ST_EMA_N,app_mng.1ST_EMA_RATIO
app_mng.2ND_EMA_AVG,app_mng.2ND_EMA_HWM,app_mng.2ND_EMA_TMO,app_mng.2ND_EMA_N,app_mng.2ND_EMA_RATIO
app_mng.3RD_EMA_AVG,app_mng.3RD_EMA_HWM,app_mng.3RD_EMA_TMO,app_mng.3RD_EMA_N,app_mng.3RD_EMA_RATIO

非常恶心的代码,而且非常容易写错,如果是python,由于其本身自省的能力,所以不会存在这样的问题,但是C++可没有这种能力,所以我们只能寄希望与宏定义了。
直接来看一下我们改写的代码:

#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <map>
using namespace std;
class EMA
{
    public:
        EMA(string a,string b,string c,string d,string e)
        {
            cout <<a<<","<<b<<","<<c<<","<<d<<","<<e<<endl;
        }
};
#define EMACLASS_DEFINITION(class_name)\
    class EMA4CGI_##class_name:public EMA{\
        public:\
            EMA4CGI_##class_name():EMA(\
                    "app_mng."#class_name"_EMA_AVG",\
                    "app_mng."#class_name"_EMA_HWM",\
                    "app_mng."#class_name"_EMA_TMO",\
                    "app_mng."#class_name"_EMA_N",\
                    "app_mng."#class_name"_EMA_RATIO"\
                    ){}\
            ~EMA4CGI_##class_name() {}\
    };
 
EMACLASS_DEFINITION(1ST)
EMACLASS_DEFINITION(2ND)
EMACLASS_DEFINITION(3RD)
 
int main(int argc, const char *argv[])
{
    EMA4CGI_1ST();
    EMA4CGI_2ND();
    EMA4CGI_3RD();
    return 0;
}
输入结果为:
app_mng.1ST_EMA_AVG,app_mng.1ST_EMA_HWM,app_mng.1ST_EMA_TMO,app_mng.1ST_EMA_N,app_mng.1ST_EMA_RATIO
app_mng.2ND_EMA_AVG,app_mng.2ND_EMA_HWM,app_mng.2ND_EMA_TMO,app_mng.2ND_EMA_N,app_mng.2ND_EMA_RATIO
app_mng.3RD_EMA_AVG,app_mng.3RD_EMA_HWM,app_mng.3RD_EMA_TMO,app_mng.3RD_EMA_N,app_mng.3RD_EMA_RATIOOK,

可能问题本身在不同的场景下有多种解决方式,但是这至少提供了另一个看问题的角度,希望对大家有用。