linux c 获取网关ip

ip route show default | awk '/default/ {print $3}'

route -n | grep 'UG[ \t]' | awk '{print $2}'

netstat -rn | grep '^default' | awk '{print $2}'

grep 'gateway' /etc/network/interfaces | awk '{print $2}'

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

int get_gateway_ip(char *gateway_ip, size_t size) {
    FILE *fp;
    char line[256];
    char *token;

    fp = popen("ip route show default", "r");
    if (fp == NULL) {
        perror("popen");
        return -1;
    }

    while (fgets(line, sizeof(line), fp)) {
        token = strtok(line, " ");
        while (token != NULL) {
            if (strcmp(token, "default") == 0) {
                token = strtok(NULL, " ");
                if (token != NULL) {
                    strncpy(gateway_ip, token, size);
                    gateway_ip[size - 1] = '\0';
                    pclose(fp);
                    return 0;
                }
            }
            token = strtok(NULL, " ");
        }
    }

    pclose(fp);
    return -1;
}

int main() {
    char gateway_ip[16];
    if (get_gateway_ip(gateway_ip, sizeof(gateway_ip)) == 0) {
        printf("Gateway IP: %s\n", gateway_ip);
    } else {
        printf("Failed to get gateway IP.\n");
    }
    return 0;
}