获取 Linux 上接口的 IP 地址

问题描述：

如何从 C 代码获取 Linux 上接口的IPv4地址？

例如，我想要获取分配给 eth0 的 IP 地址（如果有）。

解决方案 1：

尝试一下：

#include <stdio.h>
#include <unistd.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>
#include <arpa/inet.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 */
 printf("%s
", inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));

 return 0;
}

代码示例取自这里。

解决方案 2：

ioctl()除了Filip 演示的方法之外，您还可以使用getifaddrs ()。手册页底部有一个示例程序。

解决方案 3：

如果你正在寻找特定接口（比如wlan0）的地址（IPv4） ，那么尝试使用getifaddrs()的这段代码：

#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[])
{
    struct ifaddrs *ifaddr, *ifa;
    int family, s;
    char host[NI_MAXHOST];

    if (getifaddrs(&ifaddr) == -1) 
    {
        perror("getifaddrs");
        exit(EXIT_FAILURE);
    }


    for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) 
    {
        if (ifa->ifa_addr == NULL)
            continue;  

        s=getnameinfo(ifa->ifa_addr,sizeof(struct sockaddr_in),host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);

        if((strcmp(ifa->ifa_name,"wlan0")==0)&&(ifa->ifa_addr->sa_family==AF_INET))
        {
            if (s != 0)
            {
                printf("getnameinfo() failed: %s
", gai_strerror(s));
                exit(EXIT_FAILURE);
            }
            printf("    Interface : <%s>
",ifa->ifa_name );
            printf("      Address : <%s>
", host); 
        }
    }

    freeifaddrs(ifaddr);
    exit(EXIT_SUCCESS);
}

您可以将wlan0替换为eth0（表示以太网）和lo（表示本地环回）。

所用数据结构的结构和详细解释可在此处找到。

要了解有关 C 中的链表的更多信息，此页面将是一个很好的起点。

解决方案 4：

我的看法：即使在 iOS 上，同样的代码也能正常工作：

#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>



#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    showIP();
}



void showIP()
{
    struct ifaddrs *ifaddr, *ifa;
    int family, s;
    char host[NI_MAXHOST];

    if (getifaddrs(&ifaddr) == -1)
    {
        perror("getifaddrs");
        exit(EXIT_FAILURE);
    }


    for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
    {
        if (ifa->ifa_addr == NULL)
            continue;

        s=getnameinfo(ifa->ifa_addr,sizeof(struct sockaddr_in),host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);

        if( /*(strcmp(ifa->ifa_name,"wlan0")==0)&&( */ ifa->ifa_addr->sa_family==AF_INET) // )
        {
            if (s != 0)
            {
                printf("getnameinfo() failed: %s
", gai_strerror(s));
                exit(EXIT_FAILURE);
            }
            printf("    Interface : <%s>
",ifa->ifa_name );
            printf("      Address : <%s>
", host);
        }
    }

    freeifaddrs(ifaddr);
}


@end

我只是删除了针对 wlan0 的测试来查看数据。ps 您可以删除“family”

解决方案 5：

我最近也遇到了同样的问题，这是我编写的代码，它可以正常工作。请确保使用网络接口的名称，与您拥有的名称完全一致（可以是“eth0”或其他）。

必须ifconfig事先检查命令以获取接口名称并在 C 中使用它。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <unistd.h>
#include <linux/if.h>
#include <errno.h>
#include <ifaddrs.h>
#include <netinet/in.h>
#include <arpa/inet.h>
    

void extract_ipaddress()
    {
        //create an ifreq struct for passing data in and out of ioctl
        struct ifreq my_struct;
     
        //declare and define the variable containing the name of the interface
        char *interface_name="enp0s3";   //a very frequent interface name is "eth0";
     
        //the ifreq structure should initially contains the name of the interface to be queried. Which should be copied into the ifr_name field.
        //Since this is a fixed length buffer, one should ensure that the name does not cause an overrun
        size_t interface_name_len=strlen(interface_name);
     
        if(interface_name_len<sizeof(my_struct.ifr_name))
        {
            memcpy(my_struct.ifr_name,interface_name,interface_name_len);
            my_struct.ifr_name[interface_name_len]=0;
        }
        else
        {
            perror("Copy name of interface to ifreq struct");
            printf("The name you provided for the interface is too long...
");
        }
     
        //provide an open socket descriptor with the address family AF_INET
        /* ***************************************************************
         * All ioctl call needs a file descriptor to act on. In the case of SIOCGIFADDR this must refer to a socket file descriptor. This socket must be in the address family that you wish to obtain (AF_INET for IPv4)
         * ***************************************************************
         */
     
        int file_descriptor=socket(AF_INET, SOCK_DGRAM,0);
     
        if(file_descriptor==-1)
        {
            perror("Socket file descriptor");
            printf("The construction of the socket file descriptor was unsuccessful.
");
            return -1;
        }
     
        //invoke ioctl() because the socket file descriptor exists and also the struct 'ifreq' exists
        int myioctl_call=ioctl(file_descriptor,SIOCGIFADDR,&my_struct);
     
        if (myioctl_call==-1)
        {
            perror("ioctl");
            printf("Ooops, error when invoking ioctl() system call.
");
            close(file_descriptor);
            return -1;
        }
     
        close(file_descriptor);
     
        /* **********************************************************************
         * If this completes without error , then the hardware address of the interface should have been returned in the  'my_struct.ifr_addr' which is types as struct sockaddr_in.
         * ***********************************************************************/
     
      //extract the IP Address (IPv4) from the my_struct.ifr_addr which has the type 'ifreq'
     
        /* *** Cast the returned address to a struct 'sockaddr_in' *** */
        struct sockaddr_in * ipaddress= (struct sockaddr_in *)&my_struct.ifr_addr;
       /* *** Extract the 'sin_addr' field from the data type (struct) to obtain a struct 'in_addr' *** */
      printf("IP Address is %s.
", inet_ntoa(ipaddress->sin_addr));

    }

解决方案 6：

如果您不介意二进制大小，您可以使用 iproute2 作为库。

iproute2-as-lib

优点：

• 不需要编写socket层代码。

• 可以获取有关网络接口的更多甚至更多信息。与 iproute2 工具具有相同的功能。

• 简单的API接口。

缺点：

• iproute2-as-lib 库很大。~500kb。

解决方案 7：

我发现了一个获取 ip 的相当简单的方法，利用 bash 命令：

hostname -I

但是使用“hostname -I”本身会在屏幕上打印结果，我们需要使用“popen()”读取结果并将其保存为字符串，这里是 c 代码：

#include <stdio.h> // popen
#include "ip_common_def.h"

const char * get_ip()
{
    // Read out "hostname -I" command output
    FILE *fd = popen("hostname -I", "r");
    if(fd == NULL) {
    fprintf(stderr, "Could not open pipe.
");
    return NULL;
    }
    // Put output into a string (static memory)
    static char buffer[IP_BUFFER_LEN];
    fgets(buffer, IP_BUFFER_LEN, fd);

    // Only keep the first ip.
    for (int i = 0; i < IP_BUFFER_LEN; ++i)
    {
        if (buffer[i] == ' ')
        {
            buffer[i] = '';
            break;
        }
    }

    char *ret = malloc(strlen(buffer) + 1);
    memcpy(ret, buffer, strlen(buffer));
    ret[strlen(buffer)] = '';
    printf("%s
", ret);
    return ret;
}