/**decode编码*/
- (NSString *)encodeToPercentEscapeString
{
    NSString*
    outputStr = (__bridge NSString *)CFURLCreateStringByAddingPercentEscapes(
                                                                             
                                                                             NULL, /* allocator */
                                                                             
                                                                             (__bridge CFStringRef)self,
                                                                             
                                                                             NULL, /* charactersToLeaveUnescaped */
                                                                             
                                                                             (CFStringRef)@"!*'();:@&=+$,/?%#[]",
                                                                             
                                                                             kCFStringEncodingUTF8);
    
    
    return
    outputStr;
}
/**decode解码*/
- (NSString *)decodeFromPercentEscapeString
{
    NSMutableString *outputStr = [NSMutableString stringWithString:self];
    [outputStr replaceOccurrencesOfString:@"+"
                               withString:@""
                                  options:NSLiteralSearch
                                    range:NSMakeRange(0,[outputStr length])];
    return
    [outputStr stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
}

网站题目：IOSencode解码与编码
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