get_local_ip.c

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


int GetLocalIp(char* buffer, size_t buflen) 
{
    if (buflen < 16) {
        return 1;
    }

    int sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sock) {
        return 1;
    }

    const char* remoteIp = "10.255.255.255";
    uint16_t port = 53;

    struct sockaddr_in serv;
    memset(&serv, 0, sizeof(serv));
    serv.sin_family = AF_INET;
    serv.sin_addr.s_addr = inet_addr(remoteIp);
    serv.sin_port = htons(port);

    int err = connect(sock, (const struct sockaddr*) &serv, sizeof(serv));
    if (0 != err) {
        return 1;
    }

    struct sockaddr_in name;
    socklen_t namelen = sizeof(name);
    err = getsockname(sock, (struct sockaddr*) &name, &namelen);
    if (0 != err) {
        return 1;
    }

    if(NULL == inet_ntop(AF_INET, &name.sin_addr, buffer, buflen)) {
        return 1;
    }

    close(sock);
    return 0;
}

int main(int argc, char* argv[]) {

    char buffer[32] = "";

    GetLocalIp(buffer, sizeof(buffer));
    printf("local ip: %s\n", buffer);

    return 0;
}