Using compiler constants in C + + to replace preprocessing constants

For simple constants that are preprocessed, the const type can be used instead;

In object-oriented programming, constants within a class can be replaced with static const members.

Note within the class (In-class), the static const member only allows an integer constant to be assigned, if the other type is declared within the class, and the method is defined outside the class;

You can also use the "enum hack" to provide a const effect and give a built-in (built-in) array declaration;

There are many problems in preprocessing function call, which can be replaced by template inline (template inline), and it can achieve high efficiency.

See code specifically, and comments;

Code (/*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 <algo  
      
Rithm> using namespace std; #define Aspect_ratio 1.653//aspect ratio/* More Highlights: 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; Cannot initialize non-integral enum {enumturns = 5} in class;  
    Enumeration type Std::array<int, numturns> scores;  
Std::array<int, enumturns> escores;  
};  
      
Const DOUBLE Gameplayer::P i = 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) {   
    Preprocessor definition std::cout << "aspect_ratio =" << aspect_ratio << Std::endl;  
    Constant Definition const Double aspectratio = 1.653;  
      
    Std::cout << "aspectratio =" << aspectratio << Std::endl;  
    Constant Pointer const char* CONST AUTHORNAME = "Caroline";  
      
    Std::cout << "AuthorName =" << authorname << Std::endl;  
    Constant Pointer const std::string sauthorname ("Caroline");  
      
    Std::cout << "sauthorname =" << sauthorname << Std::endl;  
    Class exclusive constant 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::P i =" << gameplayer::P i << Std::endl;  
    TEST macro int a = 5, b = 0; Call_With_max (++a, b); A, + + two times std::cout << ";  
    A = "<< a <<std::endl;  
    A = 5, b = 0; Call_with_max (++a, b+10); A, + + once std::cout << ";  
      
    A = "<< a <<std::endl;  
    Template inline A = 5, b = 0;  
    Callwithmax (++a, b); Std::cout << ";  
      
    A = "<< a <<std::endl;  
      
return 0; }

Output:

Aspect_ratio = 1.653  
aspectratio = 1.653  
authorname = Caroline sauthorname  
= Caroline gp.scores:1  
2 3 4 5   
gameplayer::P i = 3.14  
f:7; a = 7  
f:10; a = 6  
f:6; a = 6

Author: csdn Blog spike_king