numb2string

有了上一篇的str2type,类似的可以定义numb2string

1.定义

 1 namespace blog
 2 {
 3     namespace internal{
 4         template< std::size_t N, std::size_t M >
 5         constexpr char string_at(const char(&c)[M]) noexcept
 6         {
 7             static_assert(M <= 101, "String longer than 100 (excluding terminating \\0)!");
 8             return (N < M) ? c[N] : 0;
 9         }
10
11         template< char ... Cs > struct string;
12
13         template<> struct string<> {};
14
15         template< char ... Cs >
16         struct string
17         {
18             static constexpr char const value[sizeof...(Cs)+1] = { Cs...,‘\0‘ };
19         };
20         template<char... C>
21         constexpr char const string<C...>::value[sizeof...(C)+1];
22     }
23     template< char ... Cs > struct string : internal::string< Cs ... > {};
24
25     namespace internal
26     {
27         template< typename, char ... >
28         struct number_string_builder;
29
30         template< typename T >
31         struct number_string_builder< T > { using type = T; };
32         template< template< char ... > class S, char ... Hs, char C, char ... Cs >
33         struct number_string_builder< S< Hs ... >, C, Cs ... >
34             : std::conditional< C == ‘a‘,
35             number_string_builder< S< Hs ... > >,
36             number_string_builder< S< C, Hs ...>, Cs ... > >::type { };
37
38         template< typename, char ... >
39         struct string_builder;
40         template< typename T >
41         struct string_builder< T > { using type = T; };
42         template< template< char ... > class S, char ... Hs, char C, char ... Cs >
43         struct string_builder< S< Hs ... >, C, Cs ... >
44             : std::conditional< C == ‘\0‘,
45             string_builder< S< Hs ... > >,
46             string_builder< S< Hs ..., C >, Cs ... > >::type
47         { };
48     }
49 }

2.实现

 1 #define blog_numb2str(n)  2         blog::internal::number_string_builder< blog::internal::string<>, ‘0‘ + n%10,  3                     n/10 == 0 ? ‘a‘ : ‘0‘ + (n/10)%10,  4                     n/100 == 0 ? ‘a‘ : ‘0‘ + (n/100)%10,  5                     n/1000 == 0 ? ‘a‘ : ‘0‘ + (n/1000)%10,  6                     n/10000 == 0 ? ‘a‘ : ‘0‘ + (n/10000)%10,  7                     n/100000 == 0 ? ‘a‘ : ‘0‘ + (n/100000)%10,  8                     n/1000000 == 0 ? ‘a‘ : ‘0‘ + (n/1000000)%10,  9                     n/10000000 == 0 ? ‘a‘ : ‘0‘ + (n/10000000)%10, 10                     n/100000000 == 0 ? ‘a‘ : ‘0‘ + (n/100000000)%10, 11                     n/1000000000 == 0 ? ‘a‘ : ‘0‘ + (n/1000000000)%10, 12                     n/10000000000 == 0 ? ‘a‘ : ‘0‘ + (n/10000000000)%10 >::type::value

3.使用

1 std::cout << blog_numb2str(12345678) << std::endl; 

4.结果

12345678

5.优缺点