//以目錄枚舉為例子，說明enumerator，從源碼剝離可運行

#include <stdio.h>
#include <stdbool.h>
#include <dirent.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
#include <sys/time.h>
#include <stdarg.h>/*** This macro allows counting the number of arguments passed to a macro.* Combined with the VA_ARGS_DISPATCH() macro this can be used to implement* macro overloading based on the number of arguments.* 0 to 10 arguments are currently supported.*/
#define VA_ARGS_NUM(...) _VA_ARGS_NUM(0,##__VA_ARGS__,10,9,8,7,6,5,4,3,2,1,0)
#define _VA_ARGS_NUM(_0,_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,NUM,...) NUM/*** This macro can be used to dispatch a macro call based on the number of given* arguments, for instance:** @code* #define MY_MACRO(...) VA_ARGS_DISPATCH(MY_MACRO, __VA_ARGS__)(__VA_ARGS__)* #define MY_MACRO1(arg) one_arg(arg)* #define MY_MACRO2(arg1,arg2) two_args(arg1,arg2)* @endcode** MY_MACRO() can now be called with either one or two arguments, which will* resolve to one_arg(arg) or two_args(arg1,arg2), respectively.*/
#define VA_ARGS_DISPATCH(func, ...) _VA_ARGS_DISPATCH(func, VA_ARGS_NUM(__VA_ARGS__))
#define _VA_ARGS_DISPATCH(func, num) __VA_ARGS_DISPATCH(func, num)
#define __VA_ARGS_DISPATCH(func, num) func ## num/*** Assign variadic arguments to the given variables.** @note The order and types of the variables are significant and must match the* variadic arguments passed to the function that calls this macro exactly.** @param last		the last argument before ... in the function that calls this* @param ...		variable names*/
#define VA_ARGS_GET(last, ...) ({ \va_list _va_args_get_ap; \va_start(_va_args_get_ap, last); \_VA_ARGS_GET_ASGN(__VA_ARGS__) \va_end(_va_args_get_ap); \
})/*** Assign variadic arguments from a va_list to the given variables.** @note The order and types of the variables are significant and must match the* variadic arguments passed to the function that calls this macro exactly.** @param list		the va_list variable in the function that calls this* @param ...		variable names*/
#define VA_ARGS_VGET(list, ...) ({ \va_list _va_args_get_ap; \va_copy(_va_args_get_ap, list); \_VA_ARGS_GET_ASGN(__VA_ARGS__) \va_end(_va_args_get_ap); \
})#define _VA_ARGS_GET_ASGN(...) VA_ARGS_DISPATCH(_VA_ARGS_GET_ASGN, __VA_ARGS__)(__VA_ARGS__)
#define _VA_ARGS_GET_ASGN1(v1) __VA_ARGS_GET_ASGN(v1)
#define _VA_ARGS_GET_ASGN2(v1,v2) __VA_ARGS_GET_ASGN(v1) __VA_ARGS_GET_ASGN(v2)
#define _VA_ARGS_GET_ASGN3(v1,v2,v3) __VA_ARGS_GET_ASGN(v1) __VA_ARGS_GET_ASGN(v2) \__VA_ARGS_GET_ASGN(v3)
#define _VA_ARGS_GET_ASGN4(v1,v2,v3,v4) __VA_ARGS_GET_ASGN(v1) __VA_ARGS_GET_ASGN(v2) \__VA_ARGS_GET_ASGN(v3) __VA_ARGS_GET_ASGN(v4)
#define _VA_ARGS_GET_ASGN5(v1,v2,v3,v4,v5) __VA_ARGS_GET_ASGN(v1) __VA_ARGS_GET_ASGN(v2) \__VA_ARGS_GET_ASGN(v3) __VA_ARGS_GET_ASGN(v4) __VA_ARGS_GET_ASGN(v5)
#define __VA_ARGS_GET_ASGN(v) v = va_arg(_va_args_get_ap, typeof(v));#ifndef FALSE
# define FALSE false
#endif /* FALSE */
#ifndef TRUE
# define TRUE  true
#endif /* TRUE */typedef struct enumerator_t enumerator_t;struct enumerator_t {/*** 枚舉集合。** enumerate（） 方法接受可變數量的指針參數(枚舉到的值被寫入這些參數)**通常只需分配調用枚舉器的 venumerate（） 方法的通用 enumerator_enumerate_default（） 函數就足夠了。 ...** @param ...	枚舉項的變量列表，取決于實現* @return		TRUE if pointers returned*/bool (*enumerate)(enumerator_t *this, ...);/*** 枚舉集合。** venumerate（） 方法采用一個變量參數列表，其中包含將枚舉值寫入的指針。** @param args	枚舉項的變量列表，取決于實現* @return		TRUE if pointers returned*/bool (*venumerate)(enumerator_t *this, va_list args);/*** Destroy an enumerator_t instance.*/void (*destroy)(enumerator_t *this);
};/*** Enumerator implementation for directory enumerator*/
typedef struct {/** implements enumerator_t */enumerator_t public;/** directory handle */DIR *dir;/** absolute path of current file */char full[PATH_MAX];/** where directory part of full ends and relative file gets written *///完整路徑中的目錄部分結束以及相對文件將被寫入的位置char *full_end;
} dir_enum_t;
/*** Helper function that compares two strings for equality*/
static inline bool streq(const char *x, const char *y)
{return (x == y) || (x && y && strcmp(x, y) == 0);
}bool enumerate_dir_enum(dir_enum_t *this, va_list args){//讀取目錄中的條目,依靠此函數特性實現枚舉struct dirent *entry = readdir(this->dir);struct stat *st = NULL;size_t remaining;char **relative = NULL, **absolute = NULL;;int len;//對應enumerate輸入的變參... &relative, &file, NULL 下面寫入這些值相當于寫入那些值VA_ARGS_VGET(args, relative, absolute, st);if (!entry){return FALSE;}if (streq(entry->d_name, ".") || streq(entry->d_name, "..")){return this->public.enumerate(&this->public, relative, absolute, st);}if (relative){//條目名稱*relative = entry->d_name;}if (absolute || st){//full是路徑,relativeremaining = sizeof(this->full) - (this->full_end - this->full);len = snprintf(this->full_end, remaining, "%s", entry->d_name);if (len < 0 || len >= remaining){return FALSE;}if (absolute){*absolute = this->full;}if (st && stat(this->full, st)){/* try lstat() e.g. if a symlink is not valid anymore */if ((errno != ENOENT && errno != ENOTDIR) || lstat(this->full, st)){return FALSE;}}}return TRUE;
}# define DIRECTORY_SEPARATOR "/"
static inline bool path_is_separator(char c)
{return c == DIRECTORY_SEPARATOR[0];
}/*** Object allocation/initialization macro, using designated initializer.*/
#define INIT(this, ...) ({ (this) = malloc(sizeof(*(this))); \*(this) = (typeof(*(this))){ __VA_ARGS__ }; (this); })bool enumerator_enumerate_default(enumerator_t *enumerator, ...)
{va_list args;bool result;if (!enumerator->venumerate){return FALSE;}//va_start用于獲取函數參數列表...中可變參數的首指針//輸出參數args保存函數參數列表中可變參數的首指針(即,可變參數列表)//輸入參數enumerator為函數參數列表中最后一個固定參數(...之前)va_start(args, enumerator);result = enumerator->venumerate(enumerator, args);va_end(args);return result;
}void destroy_dir_enum(dir_enum_t *this){closedir(this->dir);free(this);
}enumerator_t* enumerator_create_directory(const char *path)
{dir_enum_t *this;int len;//實例化INIT(this,.public = {.enumerate = enumerator_enumerate_default,.venumerate = enumerate_dir_enum,.destroy = destroy_dir_enum,},);if (*path == '\0'){path = "./";}len = snprintf(this->full, sizeof(this->full)-1, "%s", path);if (len < 0 || len >= sizeof(this->full)-1){free(this);return NULL;}/* append a '/' if not already done */if (!path_is_separator(this->full[len-1])){this->full[len++] = DIRECTORY_SEPARATOR[0];this->full[len] = '\0';}this->full_end = &this->full[len];//打開目錄this->dir = opendir(path);if (!this->dir){free(this);return NULL;}return &this->public;
}int main()
{char *file;char *relative;char *st;char *path = "/root/open/strongswan-6.0.0";enumerator_t *enumerator;enumerator = enumerator_create_directory(path);if (enumerator){while (enumerator->enumerate(enumerator, &relative, &file, NULL)){printf("file: %s | relative: %s | size:%s\n", file, relative, NULL);}enumerator->destroy(enumerator);}return 0;
}