在Vimer的程式世界 [ http://www.vimer.cn ]中看到這篇文章,對宏有了一個更深刻的瞭解,所以轉載過來以便以後學習。
============== 以下為轉載內容 ==============
今天在工作上遇到一個問題,覺得很有代表性,特抽象如下:
通過設計模式的角度來說,就是模板方法,已經有一個基類,需要定義很多子類來實現其方法。
但是類名都只有一部分不同,且建構函式的入參也只有一部分不同。
如代碼:
#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;
}
輸出如下:
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
非常噁心的代碼,而且非常容易寫錯,如果是python,由於其本身自省的能力,所以不會存在這樣的問題,但是C++可沒有這種能力,所以我們只能寄希望與宏定義了。
直接來看一下我們改寫的代碼:
#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;
}
輸入結果為:
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
OK,問題解決!
可能問題本身在不同的情境下有多種解決方式,但是這至少提供了另一個看問題的角度,希望對大家有用。
本文轉載自Vimer的程式世界 [ http://www.vimer.cn ]
原文連結地址: 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