+ (BOOL)connectedToNetwork{       //创建零地址，0.0.0.0的地址表示查询本机的网络连接状态               struct sockaddr_storage zeroAddress;//IP地址               bzero(&zeroAddress, sizeof(zeroAddress));//将地址转换为0.0.0.0       zeroAddress.ss_len = sizeof(zeroAddress);//地址长度       zeroAddress.ss_family = AF_INET;//地址类型为UDP, TCP, etc.               // Recover reachability flags       SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);       SCNetworkReachabilityFlags flags;               //获得连接的标志       BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);       CFRelease(defaultRouteReachability);               //如果不能获取连接标志，则不能连接网络，直接返回       if (!didRetrieveFlags)          {            return NO;        }       //根据获得的连接标志进行判断           BOOL isReachable = flags & kSCNetworkFlagsReachable;       BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;       return (isReachable&&!needsConnection) ? YES : NO;        /*     1、sockaddr_storage     This structure stores socket address information. Because this structure is large enough to store IPv4 or IPv6 address information, its use promotes protocol-family and protocol-version independence, and simplifies cross-platform development. Use this structure in place of the sockaddr structure.          2、     extern void bzero（void *s, int n）;     用法：#include <string.h>     功能：置字节字符串s的前n个字节为零且包括‘\0’。     说明：bzero无返回值，并且使用string.h头文件，string.h曾经是posix标准的一部分，但是在POSIX.1-2001标准里面，     这些函数被标记为了遗留函数而不推荐使用。在POSIX.1-2008标准里已经没有这些函数了。推荐使用memset替代bzero。          bzero( &tt, sizeof( tt ) );      //等价于memset(&tt,0,sizeof(tt));     bzero( s, 20 );                  //等价于memset(s,0,20);          */}

-(BOOL)isConnectionAvailable{        BOOL isExistenceNetwork = YES;    Reachability *reach = [Reachability reachabilityWithHostName:@"http://www.baidu.com"];    switch ([reach currentReachabilityStatus]) {        case NotReachable:            isExistenceNetwork = NO;            //NSLog(@"notReachable");            break;        case ReachableViaWiFi:            isExistenceNetwork = YES;            //NSLog(@"WIFI");            break;        case ReachableViaWWAN:            isExistenceNetwork = YES;            //NSLog(@"3G");            break;    }            return isExistenceNetwork;}