C语言实现ifconfig

在C语言中，可以使用系统库函数和网络编程库函数来实现ifconfig的功能。以下是一个基本的示例代码，用于获取本地网络接口信息：

#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char *argv[]) {
    struct ifreq ifr;
    struct ifconf ifc;
    char buf[1024];
    int success = 0;

    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (sock == -1) {
        printf("Error: could not create socket\n");
        exit(1);
    }

    ifc.ifc_len = sizeof(buf);
    ifc.ifc_buf = buf;
    if (ioctl(sock, SIOCGIFCONF, &ifc) == -1) {
        printf("Error: could not get network interface configuration\n");
        exit(1);
    }

    struct ifreq *ifr_ptr = ifc.ifc_req;
    for (int i = ifc.ifc_len / sizeof(struct ifreq); i > 0; i--) {
        if (strcmp(ifr_ptr->ifr_name, "lo") != 0) {
            memcpy(&ifr, ifr_ptr, sizeof(struct ifreq));

            if (ioctl(sock, SIOCGIFFLAGS, &ifr) == 0) {
                if (ifr.ifr_flags & IFF_UP) {
                    printf("%s: UP\n", ifr.ifr_name);

                    if (ioctl(sock, SIOCGIFADDR, &ifr) == 0) {
                        struct sockaddr_in *addr_ptr = (struct sockaddr_in*)&ifr.ifr_addr;
                        char *addr = inet_ntoa(addr_ptr->sin_addr);
                        printf("\tIP Address: %s\n", addr);
                    }

                    if (ioctl(sock, SIOCGIFNETMASK, &ifr) == 0) {
                        struct sockaddr_in *addr_ptr = (struct sockaddr_in*)&ifr.ifr_netmask;
                        char *addr = inet_ntoa(addr_ptr->sin_addr);
                        printf("\tNetmask: %s\n", addr);
                    }

                    if (ioctl(sock, SIOCGIFMTU, &ifr) == 0) {
                        printf("\tMTU: %d\n", ifr.ifr_mtu);
                    }

                    if (ioctl(sock, SIOCGIFHWADDR, &ifr) == 0) {
                        unsigned char *mac = (unsigned char*)ifr.ifr_hwaddr.sa_data;
                        printf("\tMAC Address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                            mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
                    }

                    success = 1;
                }
            } else {
                printf("Error: could not get network interface flags\n");
            }

            printf("\n");
        }

        ifr_ptr++;
    }

    if (!success) {
        printf("Error: could not find any active network interfaces\n");
    }

    close(sock);

    return 0;
}

该代码将枚举系统上所有的网络接口，并打印它们的IP地址、子网掩码、MAC地址和MTU（最大传输单元）。要运行此程序，请在终端中使用以下命令：

gcc ifconfig.c -o ifconfig && sudo ./ifconfig

请注意，需要使用sudo权限才能访问网络接口信息。