C++中使用編譯器常量代替預先處理常量詳解

對於預先處理的單純常量, 可以使用const類型進行代替;

在物件導向編程中, 類內的常量, 可以使用靜態const成員代替,

注意類內(in-class), 靜態const成員只允許使用整型常量進行賦值, 如果是其他類型, 是在類內聲明, 類外定義的方式;

也可以使用"enum hack", 提供const的作用, 並且給內建(built-in)數組聲明;

預先處理的函數調用存在很多問題, 可以使用模板內聯(template inline)代替, 也可以獲得很高的效率;

具體參見代碼, 及注釋;

代碼(/*eclipse cdt ; gcc 4.7.1*/):

/*  * effectivecpp.cpp  *  *  Created on: 2013.11.13  *      Author: Caroline  */      /*eclipse cdt ; gcc 4.7.1*/      #include <iostream>  #include <string>  #include <array>        #include <algorithm>        using namespace std;        #define ASPECT_RATIO 1.653 //長寬比  /*更多精彩內容：http://www.bianceng.cnhttp://www.bianceng.cn/Programming/cplus/*/#define CALL_WITH_MAX(a, b) f((a) > (b) ? (a) : (b))        class GamePlayer {  public:      static const int NumTurns = 5;      static const double PI ; //不能內類初始化非整型      enum {eNumTurns = 5}; //枚舉類型      std::array<int, NumTurns> scores;      std::array<int, eNumTurns> escores;  };  const double GamePlayer::PI = 3.14;        template<typename T>  void f (T a) {      std::cout << "f : " << a ;  }        template<typename T>  inline void callWithMax(const T& a, const T& b)  {      f(a>b ? a : b);  }        int main (void) {            //前置處理器定義      std::cout << "ASPECT_RATIO = " << ASPECT_RATIO << std::endl;            //常量定義      const double AspectRatio = 1.653;      std::cout << "AspectRatio = " << AspectRatio << std::endl;            //常量指標      const char* const authorName = "Caroline";      std::cout << "authorName = " << authorName << std::endl;            //常量指標      const std::string sAuthorName("Caroline");      std::cout << "sAuthorName = " << sAuthorName << std::endl;            //class專屬常量      GamePlayer gp;      std::array<int, GamePlayer::NumTurns> scores = { {1, 2, 3, 4, 5} };      gp.scores = scores;      std::cout << "gp.scores : ";      for(const auto s : gp.scores)          std::cout << s << " ";      std::cout << std::endl;      std::cout << "GamePlayer::PI = " << GamePlayer::PI << std::endl;            //測試宏      int a = 5, b = 0;      CALL_WITH_MAX(++a, b); //a, ++兩次      std::cout << " ; a = " << a <<std::endl;      a = 5, b = 0;      CALL_WITH_MAX(++a, b+10); //a, ++一次      std::cout << " ; a = " <<  a <<std::endl;            //template inline      a = 5, b = 0;      callWithMax(++a, b);      std::cout << " ; a = " << a <<std::endl;            return 0;        }

輸出:

ASPECT_RATIO = 1.653  AspectRatio = 1.653  authorName = Caroline  sAuthorName = Caroline  gp.scores : 1 2 3 4 5   GamePlayer::PI = 3.14  f : 7 ; a = 7  f : 10 ; a = 6  f : 6 ; a = 6

作者：csdn部落格 Spike_King