base64编码和解码----系统方法

//base64编码 noteStr是要编码的字符串
NSData *data = [noteStr
dataUsingEncoding:NSUTF8StringEncoding];
NSString *dataStr = [data
base64EncodedStringWithOptions:NSDataBase64EncodingEndLineWithLineFeed];
//base64解码 noteStr是要解码的字符串

NSData *base64Decoded = [[NSData
alloc]initWithBase64EncodedData:noteStr options:0];
NSString *noteStr = [[NSString
alloc]
initWithData:base64Decoded
encoding:NSUTF8StringEncoding];