高手帮忙分析下面一段C（unix）的代码，有关DNS解析的，调用了res_init()，res_query（）等函数。
#include <sys/socket.h>#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <resolv.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <iostream.h>
#include <string>
using namespace std;
extern struct __res_state _res;
#include <iostream>
#include <string>
using namespace std;
string NameServer;
string DomainName;
int ResolvDns(){
if( inet_addr(NameServer.c_str()) < 0 )
{
cout << "Ip " << NameServer.c_str() << " is invalid" << endl;
return -1;
}
int ret;
ret = res_init();
if(ret != 0 )
{
perror("init error\n");
return -1;
}
_res.retry = 1;
_res.nscount = 1;
_res.nsaddr_list[0].sin_addr.s_addr = inet_addr(NameServer.c_str());
int aslen = 1024;
u_char aswr[1024];
memset(aswr, 0, 1024);
ret = res_query(DomainName.c_str(), ns_c_in, ns_t_a, aswr, 1024);
if(ret < 0)
{
perror("query error\n");
return -1;
}
if(ret > 1024)
{
perror("answer 2 long error\n");
return -1;
}
ns_msg ns;
ns_rr rr;
int iipcount = 0;
ret = ns_initparse(aswr, ret, &ns);
iipcount = ns_msg_count(ns, ns_s_an);
in_addr in;
for(int mm=0; mm<iipcount; mm++)
{
if(ns_parserr(&ns, ns_s_an, mm, &rr) < 0)
{
perror("parse error\n");
continue;
}
if(ns_rr_type(rr) == ns_t_a)
{
in.s_addr = htonl(ns_get32(ns_rr_rdata(rr)));
cout << "ip: " << inet_ntoa(in) <<endl;
}
}
return 0;
}
int main(int argc, char **argv)
{
struct hostent* server;
if(argc != 3)
{
cout << "Usage : " << endl;
cout << " " << argv[0] << " IP DN" << endl;
cout << "IP : ip address of nameserver" << endl;
cout << "DN : domain name want to be resolved" << endl;
return -1;
}
NameServer = argv[1];
DomainName = argv[2];
ResolvDns();
return 1;
}
以上这段代码我在公司的solaris下运行正常，但是拿到客户那边的solaris下重新编译执行（在没有配置文件/etc/resolv.conf的情况下）却无法解析，但是当配置了/etc/resolv.conf（DNS）后，运行时即使你指定DNS为1.1.1.1也能成功解析。
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