写了个for_each宏，放出来给各位评审评审。

摘要: 转载请注明出处。http://www.cnblogs.com/dave_cn/

之前在编码的时候遇到几次需要将这么几个值统一处理下，当时也没有想到什么好招，就每个量都写了相同的代码，一直觉得很土，加之使用python时的for...in...的美好感觉，便写了个for_each的宏。

for_each宏能够很方便遍历一组零散的元素，而且在遍历完之后将不再需要的临时申请的空间释放掉。

set_list_m每次添加一个元素，set_list_f则会一次将所需要遍历的元素全部加入。

因为懒set_list_m宏中应该给变量加括号的也就懒着加了。

如果有问题的地方，还请各位多多指正！

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
 
struct list_t {
        void                 *value;
        struct list_t         *next;
};
 
#define set_list_m(_p, _list) \
        do { \
                if (_list == NULL) { \
                        _list = (struct list_t *)malloc(sizeof(struct list_t)); \
                        _list->next = NULL; \
                        _list->value = _p; \
                } \
                else { \
                        struct list_t *_tmp = _list; \
                        while (_tmp->next != NULL) { \
                                _tmp = _tmp->next; \
                        } \
                        _tmp->next = (struct list_t *)malloc(sizeof(struct list_t)); \
                        _tmp = _tmp->next; \
                        _tmp->next = NULL; \
                        _tmp->value = _p; \
                } \
        } \
        while (0)
 
/*
 * 写for_each宏的原由是为了方便遍历一组零散的元素(这些元素并没有通过数组/列表等组织在一起)
 * 而python中的for...in...也不停诱惑着我
 */
#define for_each(_p, _list) \
        for ( struct list_t *_tmp = (_list), *_front; \
              (_tmp != NULL) && (((_p) = _tmp->value) || 1); \
              _front = _tmp, _tmp = _tmp->next, free(_front) )
 
/*
 * struct list_t *set_list_f(void *p, ...)
 * @parameter: 需要要以NULL结束
 * @return:    返回for_each可用的list
 */
struct list_t *set_list_f(void *p, .../* NULL */)
{
        va_list arg_ptr;
        va_start(arg_ptr, p);
 
        struct list_t *_tmpnode = NULL;
        struct list_t *list = NULL;
        void *_tmpval = p;
        while (_tmpval != NULL) {
                if (_tmpnode == NULL) {
                        _tmpnode = (struct list_t *)malloc(sizeof(struct list_t));
                        list = _tmpnode;
                }
                else {
                        _tmpnode->next = (struct list_t *)malloc(sizeof(struct list_t));
                        _tmpnode = _tmpnode->next;
                }
                _tmpnode->next = NULL;
                _tmpnode->value = _tmpval;
 
                _tmpval = va_arg(arg_ptr, void *);
        }
 
        va_end(arg_ptr);
 
        return list;
}
 
int main()
{
        //////////////////////////////////////////////////////
        int a = 1, b = 2, c = 3;
 
        struct list_t *l1 = NULL;
        set_list_m(&a, l1);
        set_list_m(&b, l1);
        set_list_m(&c, l1);
 
        int *p1 = NULL;
        for_each(p1, l1) {
                printf("for_each\n");
                *p1 = 4;
        }
 
        printf("a = [%d], b = [%d], c = [%d]\n", a, b, c);
         
        //////////////////////////////////////////////////////
        a = 1, b = 2, c = 3;
 
        struct list_t *l2 = set_list_f(&a, &b, &c, NULL);
 
        int *p2 = NULL;
        for_each(p2, l2) {
                printf("for_each\n");
                *p2 = 5;
        }
 
        printf("a = [%d], b = [%d], c = [%d]\n", a, b, c);
         
        return 0;
}