c++ - C++ 中的连接宏

Question

我的 C++ 文件中有以下定义:

#define SIZE 32

我想生成以下两行:

typedef uint32_t bui
typedef uint64_t lui

第一行可以通过以下方式生成:

#define PASTER(x,y) x ## y ## _t
#define EVALUATOR(x,y)  PASTER(x,y)
#define NAME(fun, size) EVALUATOR(fun, size)

typedef NAME(uint,SIZE) bui

但是我不能生成第二行

typedef NAME(uint,SIZE*2) lui

是否可以不定义 #define DOUBLE_SIZE 64，仅使用 SIZE 宏来实现？

Answer 1

尽可能(几乎总是)优先使用模板而不是宏:

#include <cstdlib>
#include <cstdint>

struct Signed {};
struct Unsigned{};


namespace detail {
    template<class SignedNess, std::size_t Bits> struct make_int ;
    template<> struct make_int<Signed, 64> { using type = std::int64_t; };
    template<> struct make_int<Signed, 32> { using type = std::int32_t; };
    template<> struct make_int<Signed, 16> { using type = std::int16_t; };
    template<> struct make_int<Signed, 8> { using type = std::int8_t; };
    template<> struct make_int<Unsigned, 64> { using type = std::uint64_t; };
    template<> struct make_int<Unsigned, 32> { using type = std::uint32_t; };
    template<> struct make_int<Unsigned, 16> { using type = std::uint16_t; };
    template<> struct make_int<Unsigned, 8> { using type = std::uint8_t; };
}

template<class Signedness, std::size_t Bits> using make_int = typename detail::make_int<Signedness, Bits>::type;

int main()
{
    make_int<Signed, 16> x = 5;
}