CFURLCreateStringByAddingPercentEscapes

@implementation  NSString (URLEncoding)

-(NSString *)URLEncodedString
{
    NSString *result = (NSString *)CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
                                                                           (CFStringRef)self,
                                                                           CFSTR("%"),
                                                                           CFSTR(""),
                                                                           kCFStringEncodingUTF8);
    [result autorelease];
    return result;
}


@endNSString *ret  = [@"adfadfdfs%61" URLEncodedString];

    NSLog(@"ret:%@",ret);

结果

 ret:adfadfdfs%61

@endNSString *ret  = [@"adfadfdfs%61" URLEncodedString];

    NSLog(@"ret:%@",ret);

结果

%特殊字符得到保留

故该函数低三参数 用于保留特殊字符 不转换。