c-ares DNS域名异步解析成IP

//build1: g++ dns_parse_cares.cc /usr/local/lib/libcares.a -lrt  -o test //build2: g++ dns_parse_cares.cc -lcares -lrt -o test#include <time.h>#include <iostream>#include <netdb.h>#include <arpa/inet.h>#include <ares.h>#include <sys/select.h>#include <string.h>#define IP_LEN 32typedef struct {char host[64];char ip[5][IP_LEN]; int count;   }IpList;void dns_callback (void* arg, int status, int timeouts, struct hostent* hptr)  //ares  处理完成，返回DNS解析的信息{    IpList *ips = (IpList*)arg;if( ips == NULL ) return;    if(status == ARES_SUCCESS){strncpy(ips->host, hptr->h_name, sizeof(ips->host));        char **pptr=hptr->h_addr_list;for(int i=0; *pptr!=NULL && i<5; pptr++,++i){            inet_ntop(hptr->h_addrtype, *pptr, ips->ip[ips->count++], IP_LEN);        }     }else{        std::cout << "lookup failed: " << status << std::endl;    }}void dns_resolve(const char* host, IpList &ips){    ares_channel channel;    // 创建一个ares_channel        int res;    if((res = ares_init(&channel)) != ARES_SUCCESS) {     // ares 对channel 进行初始化        std::cout << "ares feiled: " << res << std::endl;        return;    }//set dns server    ares_set_servers_csv(channel, "114.114.114.114");    //get host by name    ares_gethostbyname(channel, host, AF_INET, dns_callback, (void*)(&ips));    int nfds;      fd_set readers, writers;      timeval tv, *tvp;      while (true)     {          FD_ZERO(&readers);          FD_ZERO(&writers);          nfds = ares_fds(channel, &readers, &writers);   //获取ares channel使用的FD          if (nfds == 0) break;          tvp = ares_timeout(channel, NULL, &tv);              select(nfds, &readers, &writers, NULL, tvp);   //将ares的SOCKET FD 加入事件循环          ares_process(channel, &readers, &writers);  // 有事件发生 交由ares 处理    }    ares_destroy(channel);}int main(int argc, char **argv){    int res;    if(argc < 2 ) {        std::cout << "usage: " << argv[0] << " ip.address"<< std::endl;        return 1;    }IpList ips;do{memset(&ips, 0, sizeof(ips));        dns_resolve(argv[1],ips);std::cout <<"hostname:"<< ips.host << std::endl;    for(int i=0; i < ips.count; ++i){std::cout<< "address ip:" << ips.ip[i] << std::endl;}std::cout<< std::endl;}while(true);    return 0;}