网络编程 getaddrinfo 函数
解析网址，返回IP地址。
例子：
#include <iostream>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>//结构体addrinfo, in_addr
#include <netinet/in.h>
#include <arpa/inet.h>
using namespace std;
int main(){
char* hostname = "www.cnblogs.com";//博客园的网址，返回实际IP地址
addrinfo hints, *res;
in_addr addr;
int err;
memset(&hints, 0, sizeof(addrinfo));
hints.ai_socktype = SOCK_STREAM;
hints.ai_family = AF_INET;
if((err = getaddrinfo(hostname, NULL, &hints, &res)) != 0){
printf("error %d : %s\n", err, gai_strerror(err));
return 1;
}
addr.s_addr = ((sockaddr_in*)(res->ai_addr))->sin_addr.s_addr;
printf("ip addresss: %s\n", inet_ntoa(addr));//博客园的网址，返回实际IP地址
freeaddrinfo(res);
return 0;
}