宏的一些使用技巧

其实很不想写这个，尤其是大多数的宏都要写在header里，但是宏有时候真的能少些很多代码。。。

这种预编译生效的文本替换，属实是有点ugly了

enum to string

#include <stdio.h>
#include <string.h>

#define NUMARGS(...) (sizeof((int[]){__VA_ARGS__}) / sizeof(int))

#define ENUM_TO_STRING(ENUM_NAME, ...)                                         \
  enum ENUM_NAME { __VA_ARGS__ };                                              \
  char ENUM_NAME##_strings[] = #__VA_ARGS__;                                   \
  long ENUM_NAME##strings_indices[NUMARGS(__VA_ARGS__)];                       \
  char *ENUM_NAME##_to_string(enum ENUM_NAME value) {                          \
    static int init = 0;                                                       \
    if (init == 0) {                                                           \
      int n = 0;                                                               \
      ENUM_NAME##strings_indices[n++] = 0;                                     \
      char *curr_pos = strchr(ENUM_NAME##_strings, ',');                       \
      while (curr_pos) {                                                       \
        *curr_pos = '\0';                                                      \
        ENUM_NAME##strings_indices[n++] = (++curr_pos - ENUM_NAME##_strings);  \
        curr_pos = strchr(curr_pos, ',');                                      \
      }                                                                        \
      init++;                                                                  \
    }                                                                          \
    return (char *)ENUM_NAME##_strings + ENUM_NAME##strings_indices[value];    \
  }

/* Usage just create the enum */
ENUM_TO_STRING(Color, RED, GREEN, BLUE, VIOLET)

int main(void) {
  printf("%s\n", Color_to_string(RED));
  printf("%s\n", Color_to_string(BLUE));
  printf("%s\n", Color_to_string(GREEN));
  printf("%s\n", Color_to_string(VIOLET));
  printf("%s\n", Color_to_string(GREEN));
  printf("%s\n", Color_to_string(BLUE));

  return 0;
}

enum switch

#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)
#define RETURN_ENUM_STR(enum_type, x) \
  case enum_type::x:                  \
    return TOSTRING(x)

const char* ToStr(EnumType type) {
  switch(type) {
    RETURN_ENUM_STR(EnumType, kType1);
    // ...
  }
}

args count

#define _M_ARG_N(                                                              \
    _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16,     \
    _17, _18, _19, _20, _21, _22, _23, _24, _25, _26, _27, _28, _29, _30, _31, \
    _32, _33, _34, _35, _36, _37, _38, _39, _40, _41, _42, _43, _44, _45, _46, \
    _47, _48, _49, _50, _51, _52, _53, _54, _55, _56, _57, _58, _59, _60, _61, \
    _62, _63, _64, _65, _66, _67, _68, _69, _70, _71, _72, _73, _74, _75, _76, \
    _77, _78, _79, _80, _81, _82, _83, _84, _85, _86, _87, _88, _89, _90, _91, \
    _92, _93, _94, _95, _96, _97, _98, _99, _100, _101, _102, _103, _104,      \
    _105, _106, _107, _108, _109, _110, _111, _112, _113, _114, _115, _116,    \
    _117, _118, _119, _120, N, ...)                                            \
  N

#define COUNT_ARGS(...)                                                        \
  _M_ARG_N(__VA_ARGS__, 120, 119, 118, 117, 116, 115, 114, 113, 112, 111, \
           110, 109, 108, 107, 106, 105, 104, 103, 102, 101, 100, 99, 98, 97,  \
           96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80, \
           79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, \
           62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, \
           45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, \
           28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, \
           11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

反向填充展开