创建GBK编码类型

NSStringEncoding gbkEncoding =CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000); NSString*pageSource = [[NSString alloc] initWithData:pageData encoding:gbkEncoding];

为什么可以这么处理？在NSString.h（按住command，双击NSStringEncoding即能查看），对NSStringEncoding的定义中，注释这么写着：

Note that in addition to the values explicitly listed below, NSStringEncoding supports encodings provided by CFString.

See CFStringEncodingExt.h for a list of these encodings.

　See CFString.h for functions which convert between NSStringEncoding and CFStringEncoding.