初始化程序列表中的冗余宏用法 [英] Redundant macro usage in initializer lists

问题描述

使用可以成功减少代码重复之后我想进一步减少具有完全不同问题的代码重复

After I were able to successfully reduce code duplication with this I want to further reduce my code duplication with totally different problem

#include <iostream>
#include <array>

#define A1
#define B2
#define C3
#define D4
#define E5


enum Enum {
#ifdef A1
  one,
#endif
#ifdef B2
  two,
#endif
#ifdef C3
  three,
#endif
#ifdef D4
  four,
#endif
#ifdef E5
  five,
#endif
  end
};

const char* map(Enum e)
{
  switch(e)
  {
    #ifdef A1
    case one  : return "one";
    #endif
    #ifdef B2
    case two: return "two";
    #endif
    #ifdef C3
    case three : return "three";
    #endif
    #ifdef D4
    case four: return "four";
    #endif
    #ifdef E5
    case five: return "five";
    #endif
    case end: return "end";
  }
}

int main()
{
  std::array<const char*, Enum::end + 1> arr{{
    #ifdef A1
      "a",
    #endif
    #ifdef B2
      "b",
    #endif
    #ifdef C3
      "c",
    #endif
    #ifdef D4
      "d",
    #endif
    #ifdef E5
      "e",
    #endif
      "z"
  }};
  int e = 0;
  for (const auto& str : arr)
  {
    std::cout << str << " map " << map(Enum(e)) << std::endl;
    e++;
  }
  return 0;
}

请注意函数 map 在我的代码中实际上并不存在，并且仅在此示例中实现。在上面的代码中，我有两个数组，它们的值用初始化列表初始化。我要解决的问题是需要两次 #ifdef 和 #endif 。相反，我想拥有一些类似的东西

Please note the function map doesn't really exists in my code and was implemented only for this example. In the code above I have two array and their values initialized with initialization list. The problem I want to address is the need to have #ifdef and #endif twice. Instead, I want to have some thing like

#ifdef A1
#define A1_PAIR one, "a",
#else
#define A1_PAIR
#endif
#ifdef B2
#define B2_PAIR two, "b",
#else
#define B2_PAIR
#endif
#ifdef C3
#define C3_PAIR three, "c",
#else
#define C3_PAIR
#endif
#ifdef D4
#define D4_PAIR four, "d",
#else
#define D4_PAIR
#endif
#ifdef E5
#define E5_PAIR five, "e",
#else
#define E5_PAIR
#endif

#define MACRO(index) \
    A1_PAIR \
    B2_PAIR \
    C3_PAIR \
    D4_PAIR \
    E5_PAIR \
    end, "z"

enum Enum{ MACRO(1) };
std::array<const char*, Enum::end 1> arr2{{ MACRO(2) }};

显然，此代码不起作用，但我可以本着这种精神写些东西吗？

Obviously, this code doesn't work but can I write something in this spirit?

推荐答案

创建一个数组：

using arr_type=char const[];
#define ARRAY_SOURCE = arr_type{ "1", "a", "2", "b", /* etc */ }

使用 #ifdef 定义索引。

// elements.inc:
#ifdef A
ARRAY_SOURCE[0+OFFSET],
#endif
// etc

然后

std::array<const char*, NUM + 1> arr1{{
#define OFFSET 0
#include "elements.inc"
#undef OFFSET
}};
std::array<const char*, NUM + 1> arr2{{
#define OFFSET 1
#include "elements.inc"
#undef OFFSET
}};

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