for_each宏
November 19, 2010
TL;DR C语言中宏的黑魔法
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。
#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, ...)
* 需要要以NULL结束
* 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;
}
END