c ++循环宏 [英] c++ loop macros

问题描述

我使用宏编码展开循环，如下所示：（傻的例子）

  #define foreach_small_prime（p，instr）{ \ 
 int p; \ 
 p = 2; INSTR; \ 
 p = 3; INSTR; \ 
 p = 5; INSTR; \ 
 p = 7; INSTR; \ 
} 
 
 foreach_small_prime（pp，cout<< pp）; 
 
 int sum = 0; 
 foreach_small_prime（pp，{
 sum + = pp; 
 if（sum> = 10）cout << sum< endl; 
}）; 
  

但在某些情况下，我可能会使用构造：
$ b $ （int ii = 0; ii< 20; ii + = 2）

int sum = 0;
foreach_small_even（pp）{
sum + = pp;
if（sum> = 10）cout<<总和<< ENDL;



$ b我喜欢这个宏，因为我可以传递一个变量 name em>作为参数。

问题：有没有像第二个宏那样的像第一个宏一样定义循环的方法？ b $ b

解决方案

您可以查看Boost 预处理器库。它可以做各种循环的事情。语法不是很好，但我相信它的作品。但是，我自己并没有使用它。

I use macros to code unrolled loops like this: (silly example)

#define foreach_small_prime(p, instr) {   \
  int p;                                  \
  p = 2; instr;                           \
  p = 3; instr;                           \
  p = 5; instr;                           \
  p = 7; instr;                           \
}

foreach_small_prime(pp, cout << pp);

int sum = 0;
foreach_small_prime(pp, {
  sum += pp;
  if (sum >= 10) cout << sum << endl;
});

But in some cases I might use for construct:

#define foreach_small_even(ii) for(int ii = 0; ii < 20; ii += 2)

int sum = 0;
foreach_small_even(pp) {
  sum += pp;
  if (sum >= 10) cout << sum << endl;
}

I like this macros because I can pass a variable name as a parameter.

Question: Is there a way to define loop like the first one in a for-like syntax like the second macro?

解决方案

You could check out the Boost preprocessor library. It can do all sorts of looping things. The syntax isn't great, but I believe it works. I have not used it myself, however.

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