Display non printable characters

Sometimes we need to display non printable characters (ASCII code < 32 or ASCII code > 127) for debug reason. Of course we can escape the characters to hexical code, such as '\x0a\x0d', but sometimes using “Control Pictures” code page in Unicode might be a better idea, because it requires less screen space.

ASCII	Picture	Hex	HTML Entity
0	␀	2400H	␀
1	␁	2401H	␁
2	␂	2402H	␂
3	␃	2403H	␃
4	␄	2404H	␄
5	␅	2405H	␅
6	␆	2406H	␆
7	␇	2407H	␇
8	␈	2408H	␈
9	␉	2409H	␉
10	␊	240AH	␊
11	␋	240BH	␋
12	␌	240CH	␌
13	␍	240DH	␍
14	␎	240EH	␎
15	␏	240FH	␏
16	␐	2410H	␐
17	␑	2411H	␑
18	␒	2412H	␒
19	␓	2413H	␓
20	␔	2414H	␔
21	␕	2415H	␕
22	␖	2416H	␖
23	␗	2417H	␗
24	␘	2418H	␘
25	␙	2419H	␙
26	␚	241AH	␚
27	␛	241BH	␛
28	␜	241CH	␜
29	␝	241DH	␝
30	␞	241EH	␞
31	␟	241FH	␟
32	␠	2420H	␠
127	␡	2421H	␡
32	␣	2423H	␣

And here is a simple method to convert the characters in a string.

@implementation ControlPictures

+ (unichar)controlPictureByCharacter:(unichar)ch {
    if (ch < 33) {
        return (unichar)(ch + 0x2400);
    } else if (ch == 127) {
        return (unichar)0x2421;
    } else {
        return ch;
    }
}

+ (NSString *)stringByReplacingControlCharacters:(NSString *)str {
    NSMutableString *result = [@"" mutableCopy];
    for (NSInteger idx = 0; idx < str.length; idx++) {
        [result appendFormat:@"%C", [ControlPictures controlPictureByCharacter:[str characterAtIndex:idx]]];
    }
    return result;
}

@end

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