ios5之前可以通过读取配置文件获取，ios5以后苹果修改wifi列表文件位置，只有root权限才可以读取.
ios4:/System/Library/SystemConfiguration/WiFiManager.bundle/WiFiManager
ios5:/System/Library/SystemConfiguration/ipConfiguration.bundle/IPConfiguration
官方的API没有提供获取扫描所有wifi列表，相近功能的只有CaptiveNetwork，获取当前wifi的名称。
引用头文件<SystemConfiguration/CaptiveNetwork.h>
/*!
@function CNCopySupportedInterfaces
@discussion copies a list of all interfaces CaptiveNetworkSupport is monitoring.
@result An array of CFStringRef- BSD interface names.
Returns NULL if an error was encountered.
You MUST release the returned value.
*/
CFArrayRef
CNCopySupportedInterfaces(void)__OSX_AVAILABLE_STARTING(__MAC_10_8,__IPHONE_4_1);
通过CNCopySupportedInterfaces获取wifi列表，实际测试中返回数组中只有一个值，即当前连接的wifi。
- (NSString *)currentWifiSSID
{
NSString *ssid = nil;
NSArray *ifs = (__bridge id)CNCopySupportedInterfaces();
for (NSString *ifname in ifs) {
NSDictionary *info = (__bridge id)CNCopyCurrentNetworkInfo((__bridge CFStringRef)ifname);
if (info[@"SSIDD"])
{
ssid = info[@"SSID"];
}
}
return ssid;
}