This is an example to check connection state for a specific port number. It returns command output.

void* check_connection_state(void *data)
{
    uint32_t counter = 0;
    char buf[512] = {0};
    FILE *p = popen("netstat -an | grep -i PORT_NUM", "r");
    while(counter > 120 || (fread(buf, 1, sizeof(buf), p) != 0))
    {
        counter++;
        pclose(p);
        sleep(1);
        p = popen("netstat -an | grep -i PORT_NUM", "r");
    }
    pthread_exit(0);
}

int main(int argc, char* argv[])
{
    // Check connection
    pthread_t check_connection_thread;
    pthread_create (&check_connection_thread, NULL, check_connection_state, NULL);
    pthread_join(check_connection_thread, NULL);
    
    return 0;
}