strtok()和sscanf()解析字符串

strtok()
  strtok()的用法：

pstr = strtok(str, ".");
while(pstr != NULL)
{
    ip[i] = (unsigned char)atoi(pstr);

    i++;
    pstr = strtok(NULL, ".");
}

  另外，我们还可以使用sscanf()来解析一些特定字符串，如mac和ip

sscanf()
  sscanf()的举例：
  1.2str

#define MACSTR "%02x:%02x:%02x:%02x:%02x:%02x"
#define MAC2STR (a[0]&0xff), (a[1]&0xff), (a[2]&0xff), (a[3]&0xff), (a[4]&0xff), (a[5]&0xff)

ntohl(a);
#define IPSTR "%u.%u.%u.%u"
#define IP2STR(a) (a >> 24 &0xff), (a >> 16 &0xff), (a >> 8 &0xff), (a&0xff)

  2.str2

#define STR2MAC(str_mac, dest_mac) sscanf(str_mac, "%02x:%02x:%02x:%02x:%02x:%02x", dest_mac, dest_mac+1, dest_mac+2, dest_mac+3, dest_mac+4, dest_mac+5)

#define STR2IP(str_ip, dest_ip) sscanf(str_ip, "%u.%u.%u.%u", dest_ip, dest_ip+1, dest_ip+2, dest_ip+3)

  这2种写法都是错误的，是踩内存的，（即使恰巧结果是对的，也仅仅是因为所踩到的内存无关要紧罢了）。不信试着这样写：

#define STR2MAC(str_mac, dest_mac) sscanf(str_mac, "%02x:%02x:%02x:%02x:%02x:%02x", dest_mac+5, dest_mac+4, dest_mac+3, dest_mac+2, dest_mac+1, dest_mac)

#define STR2IP(str_ip, dest_ip) sscanf(str_ip, "%u.%u.%u.%u", dest_ip+3, dest_ip+2, dest_ip+1, dest_ip)

  就会发现结果错误。这是因为sscanf()的format中，要求必须严格输入，而这里%02x和%u都要求是32bit的，但输入的dest_mac和dest_ip却是unsigned char*。所以正确的宏定义：

#define STR2MAC(str_mac, dest_mac)\
do{\
    unsigned int tmp_mac[6];\
    if(sscanf(str_mac, "%02x:%02x:%02x:%02x:%02x:%02x", tmp_mac, tmp_mac+1, tmp_mac+2, tmp_mac+3, tmp_mac+4, tmp_mac+5) == 6){\
        dest_mac[0] = (unsigned char)tmp_mac[0];\
        dest_mac[1] = (unsigned char)tmp_mac[1];\
        dest_mac[2] = (unsigned char)tmp_mac[2];\
        dest_mac[3] = (unsigned char)tmp_mac[3];\
        dest_mac[4] = (unsigned char)tmp_mac[4];\
        dest_mac[5] = (unsigned char)tmp_mac[5];\
    }\
}while(0)

#define STR2IP(str_ip, dest_ip)\
do{\
    unsigned int tmp_ip[4];\
    if(sscanf(str_ip, "%u.%u.%u.%u", tmp_ip, tmp_ip+1, tmp_ip+2, tmp_ip+3) == 4){\
        *dest_ip = (tmp_ip[0]<<24) + (tmp_ip[1]<<16) + (tmp_ip[2]<<8) + tmp_ip[3];
    }\
}while(0)