MAC地址打印

Question

这是一个获取网络信息的代码，问题是当它打印MAC地址时，它会正常打印，而有时使用fff，如00:21:84:a2:12:88和00:ffffff21:84:A2:12:ffff88，则会因机器而异

以下是代码

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <time.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <sys/types.h>
#    include <netinet/if_ether.h>
#define IP_QUAD(ip)  (ip)>>24,((ip)&0x00ff0000)>>16,((ip)&0x0000ff00)>>8,((ip)&0x000000ff)
#define IP_ADDR_LEN 4
struct {
    char *dev;
    int sd;
    struct ether_addr eth;
    struct in_addr ip;
    struct in_addr bcast;
    unsigned int mtu;
} local_info ;

struct ifreq eth_init(char*,struct ifreq);
struct ifreq eth_get_info(struct ifreq);
struct ifreq eth_get_bcast(struct ifreq);

int
main(int argc,char **argv){
    int sd;
    struct ifreq ifr;
    if(argc != 2){
    fprintf(stderr,"usage: <command> <devicename>\n");
    exit(1);
    }
    ifr = eth_init(argv[1],ifr);
    ifr = eth_get_info(ifr);

    printf("> Exiting...\n");
    return(0);
}

struct ifreq
eth_init(char *dev,struct ifreq ifr){
//Intitating Socket     
if((local_info.sd = socket(PF_INET,SOCK_PACKET,(ETH_P_ALL))) < 0){
        printf("> Error initating the ethernet socket..\n");
        exit(-1);
    }
//Yupeeeeeeee Descriptor open 
    printf("> Initated Ethernet socket on Descriptor (%x)\n",local_info.sd);
//Set global variables
    local_info.dev = dev;
    return ifr;
}
struct ifreq
eth_get_info(struct ifreq ifr){
    int i = ETHER_ADDR_LEN;
    char* ptr;
    memset(&ifr,0,sizeof(ifr));
    strncpy(ifr.ifr_name,local_info.dev,sizeof(ifr.ifr_name));
    //Getting MAC
    if(ioctl(local_info.sd,SIOCGIFHWADDR,&ifr) < 0){
            printf("> Error Getting the Local Mac address\n");
            exit(-1);
        }
    printf("> Successfully received Local MAC Address : %02x:%02x:%02x:%02x:%02x:%02x\n",
                ifr.ifr_hwaddr.sa_data[0],ifr.ifr_hwaddr.sa_data[1],ifr.ifr_hwaddr.sa_data[2]
                ,ifr.ifr_hwaddr.sa_data[3],ifr.ifr_hwaddr.sa_data[4],ifr.ifr_hwaddr.sa_data[5]);

        memcpy(&(local_info.eth),&ifr.ifr_hwaddr.sa_data,ETH_ALEN);


    // Getting IP Address
        memset(&ifr,0,sizeof(ifr));
        strncpy(ifr.ifr_name,local_info.dev,sizeof(ifr.ifr_name));
        if( ioctl(local_info.sd,SIOCGIFADDR,&ifr) < 0){ 
                printf("> Error gettint the local IP address\n");
                exit(-1);
        }   
        printf("> Successfully received the IP Address %s\n",inet_ntoa((*(struct sockaddr_in *)&ifr.ifr_addr).sin_addr));
        memcpy(&(local_info.ip.s_addr),&(*(struct sockaddr_in *)&ifr.ifr_addr).sin_addr.s_addr,IP_ADDR_LEN);

            // Get MTU
        memset(&ifr,0,sizeof(ifr));
        strncpy(ifr.ifr_name,local_info.dev,sizeof(ifr.ifr_name));
        if ( ioctl(local_info.sd,SIOCGIFMTU,&ifr) < 0){
                printf("> Error Getting the MTU Value\n");
                exit(-1);
        }
        printf("> Recevied Successfully the MTU Value \n");
        local_info.mtu = ifr.ifr_mtu;


    return ifr;
}

struct ifreq
eth_get_bcast(struct ifreq ifr){
/* get broadcast addr for size */
        memset(&ifr,0,sizeof(ifr));
        strncpy(ifr.ifr_name, local_info.dev, sizeof (ifr.ifr_name));
        if (ioctl(local_info.sd, SIOCGIFBRDADDR, &ifr) < 0 ) { 
           printf("> Error getting the Broadcast address\n");
           exit(-1);
        }
        printf("> Received the BroadCast address: %s\n",inet_ntoa((*(struct sockaddr_in *)&ifr.ifr_addr).sin_addr));
        memcpy(&(local_info.bcast.s_addr),
               &(*(struct sockaddr_in *)&ifr.ifr_addr).sin_addr.s_addr,
               IP_ADDR_LEN);

    return ifr;
}

问题是eth_get_info函数的MAC扇区，打印语句

有什么解决方案吗?怎么解决？

Answer 1

这看起来像是一个已签名/未签名的问题。

尝试转换为无符号字符：

  printf("> Successfully received Local MAC Address : %02x:%02x:%02x:%02x:%02x:%02x\n",
  (unsigned char) ifr.ifr_hwaddr.sa_data[0],
  (unsigned char) ifr.ifr_hwaddr.sa_data[1],
  (unsigned char) ifr.ifr_hwaddr.sa_data[2],
  (unsigned char) ifr.ifr_hwaddr.sa_data[3],
  (unsigned char) ifr.ifr_hwaddr.sa_data[4],
  (unsigned char) ifr.ifr_hwaddr.sa_data[5]);

Answer 2

虽然这里已经有了一个公认的答案，但在netinet/ether.h中有一个更好的解决方案。

假设Mac地址通常存储在u_int8_t类型中，就像ether_addr结构中那样：

您可以简单地执行以下操作：

printf("Mac Address: %s", ether_ntoa((struct ether_addr*)ar->sa));

在我的例子中，ar看起来像这样：

struct {
   u_int8_t sa[6];
}

您可以使用类似于asprintf的命令轻松地将其复制到另一个缓冲区中

char *formatted_mac_address;
asprintf(formatted_mac_address, "Mac Address: %s", ether_ntoa((struct ether_addr*)ar->sa));

如果你没有像我这样的结构，你也可以用任何u_int8_t的地址来代替ar->sa。

应该引入适当的头/etc，但这看起来比这里接受的解决方案要整洁得多。

Answer 3

对于小于int的值，我更喜欢在格式字符串中使用显式长度修饰符。例如，对于单字节值，使用%02hhx而不是%02x。它让我不必担心那些微妙转换和升级问题：

#include <stdio.h>

int main(void)
{
    signed char sff = '\xff';
    unsigned char uff = '\xff';

    printf("signed:   %02x %02hhx\n", sff, sff);
    printf("unsigned: %02x %02hhx\n", uff, uff);

    return 0;
}

打印

signed:   ffffffff ff
unsigned: ff ff