原文

http://www.jianshu.com/p/d945454e3abc

  • res_query方法

    int res_query(char domain_name, int class, int type, char answer_buffer, int answer_buffer_length)

这是比较常见的系统调用，使用该方法的时候需要在Xcode中添加libresolv.dylib，然后包含resolv.h头文件即可，具体代码如下：

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unsigned char res[512];
    int nBytesRead = 0;

    //调用系统方法
    nBytesRead = res_query("www.baidu.com", ns_c_in, ns_t_a, res, sizeof(res));

    ns_msg handle;
    ns_initparse(res, nBytesRead, &handle);

    NSMutableArray *ipList = nil;
    int msg_count = ns_msg_count(handle, ns_s_an);
    if (msg_count > 0) {
        ipList = [[NSMutableArray alloc] initWithCapacity:msg_count];
        for(int rrnum = 0; rrnum < msg_count; rrnum++) {
            ns_rr rr;

            //解析结果
            if(ns_parserr(&handle, ns_s_an, rrnum, &rr) == 0) {
                char ip1[16];
                strcpy(ip1, inet_ntoa(*(struct in_addr *)ns_rr_rdata(rr)));
                NSString *ipString = [[NSString alloc] initWithCString:ip1 encoding:NSASCIIStringEncoding];
                if (![ipString isEqualToString:@""]) {

                    //将提取到的IP地址放到数组中
                    [ipList addObject:ipString];
                }
            }
        }
    }

然而该方法有一个问题，在网络从2/3G和WI-FI之间切换的时候，该方法经常不能正常工作，或者需要等待较长的时间，

  • gethostbyname
hostent *gethostbyname(const char *hostName);```
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具体代码如下：

struct hostent *host = gethostbyname(“www.google.com.hk”);

struct in_addr **list = (struct in_addr **)host->h_addr_list;

//获取IP地址
NSString *ip= [NSString stringWithCString:inet_ntoa(*list[0]) encoding:NSUTF8StringEncoding];

NSLog(@"ip address is : %@",ip);

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该方法在碰到切换网络的时候，出现失败的情况比上面的方法好多了，但偶尔也还是会出现，是时候采用苹果自己的方法了。

* CFHostStartInfoResolution

``` Boolean CFHostStartInfoResolution (CFHostRef theHost, CFHostInfoType info, CFStreamError *error);

具体实现方法如下:

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Boolean result,bResolved;
CFHostRef hostRef;
CFArrayRef addresses = NULL;

CFStringRef hostNameRef = CFStringCreateWithCString(kCFAllocatorDefault, "www.google.com.hk", kCFStringEncodingASCII);

hostRef = CFHostCreateWithName(kCFAllocatorDefault, hostNameRef);
if (hostRef) {
    result = CFHostStartInfoResolution(hostRef, kCFHostAddresses, NULL);
    if (result == TRUE) {
        addresses = CFHostGetAddressing(hostRef, &result);
    }
}
bResolved = result == TRUE ? true : false;

if(bResolved)
{
    struct sockaddr_in* remoteAddr;
    for(int i = 0; i < CFArrayGetCount(addresses); i++)
    {
        CFDataRef saData = (CFDataRef)CFArrayGetValueAtIndex(addresses, i);
        remoteAddr = (struct sockaddr_in*)CFDataGetBytePtr(saData);

        if(remoteAddr != NULL)
        {
            //获取IP地址
            char ip[16];
            strcpy(ip, inet_ntoa(remoteAddr->sin_addr));
        }
    }
}
CFRelease(hostNameRef);
CFRelease(hostRef);

具体的demo可以到这里看看