c - inet_ntoa 的段错误

Question

    #include <stdio.h> 
    #include <string.h> /* for strncpy */ 
    #include <sys/types.h> 
    #include <sys/socket.h> 
    #include <sys/ioctl.h> 
    #include <netinet/in.h> 
    #include <net/if.h> 

    int 
    main() 
    { 
     int fd;  
     struct ifreq ifr; 

     fd = socket(AF_INET, SOCK_DGRAM, 0);  

     /* I want to get an IPv4 IP address */ 
     ifr.ifr_addr.sa_family = AF_INET; 

     /* I want IP address attached to "eth0" */ 
     strncpy(ifr.ifr_name, "eth0", IFNAMSIZ-1); 

     ioctl(fd, SIOCGIFADDR, &ifr); 

     close(fd); 

     /* display result */ 
     char* ipaddr; 
     ipaddr = inet_ntoa(((struct sockaddr_in *)&(ifr.ifr_addr))->sin_addr); 
     printf("%s\n", ipaddr); 

     return 0; 
    } 

对于这一行:

     ipaddr = inet_ntoa(((struct sockaddr_in *)&(ifr.ifr_addr))->sin_addr);         

我明白了

iptry.c: In function ‘main’:
iptry.c:31:9: warning: assignment makes pointer from integer without a cast [enabled by default]

为了

     printf("%s\n", ipaddr);

我遇到段错误。

这是怎么回事？

Answer 1

inet_ntoa在 header 中定义 <arpa/inet.h> ,
需要#include ,否则会出错