gistfile1.m

/*
 ShiftJISのNSDataから文字コード変換してUTF-8の文字列へ
 http://d.hatena.ne.jp/koherent/20100925/1285394783
 */
// ShiftJIS data
NSDate *data = ...;
// ShiftJIS string
NSString *str = [[[NSString alloc] initWithData:data encoding:NSShiftJISStringEncoding] autorelease];

// UTF-8のchar配列を取得
const char *chars = [str cStringUsingEncoding:NSUTF8StringEncoding];
// NSStringへ変換
NSString *string = [NSString stringWithCString:chars encoding:NSUTF8StringEncoding];

gistfile2.m

// Categoryで宣言
@interface UIView (Debug)
- (NSString *)recursiveDescription;
@end

NSLog(@"%@", [self.view recursiveDescription]);

NSString_CoreAdditions.m

@implementation NSString (CoreAdditions)

/*
 URL encode
 */
- (NSString *)encodeURIComponent_NON_ARC
{
    static NSString * const kLegalCharactersToBeEscaped = @"!*'();:@&=+$,/?%#[]";
    return [(NSString *)CFURLCreateStringByAddingPercentEscapes(NULL,
                                                                (CFStringRef)self,
                                                                NULL,
                                                                (CFStringRef)kLegalCharactersToBeEscaped,
                                                                kCFStringEncodingUTF8) autorelease];
    // AFNetworking
    // static NSString * const kLegalCharactersToBeEscaped = @"?!@#$^&%*+,:;='\"`<>()[]{}/\\|~ ";
	// return [(NSString *)CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
    //                                                             (CFStringRef)[self stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
    //                                                             NULL,
    //                                                             (CFStringRef)kLegalCharactersToBeEscaped,
    //                                                             kCFStringEncodingUTF8) autorelease];

    // http://akisute.com/2008/12/cocoaiphoneurl.html
    // return (NSString *)CFURLCreateStringByAddingPercentEscapes(NULL, (CFStringRef)self, NULL, CFSTR(";,/?:@&=+$#"), kCFStringEncodingUTF8);
}

- (NSString *)decodeURIComponent_NON_ARC
{
    return [(NSString *)CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,
                                                                                (CFStringRef)self,
                                                                                CFSTR(""),
                                                                                kCFStringEncodingUTF8) autorelease];
}

- (NSString *)encodeURIComponent
{
    static NSString * const kLegalCharactersToBeEscaped = @"!*'();:@&=+$,/?%#[]";
    return (__bridge_transfer NSString *)CFURLCreateStringByAddingPercentEscapes(NULL,
                                                                                 (__bridge CFStringRef)self,
                                                                                 NULL,
                                                                                 (__bridge CFStringRef)kLegalCharactersToBeEscaped,
                                                                                 kCFStringEncodingUTF8);
}

- (NSString *)decodeURIComponent
{
    return (__bridge_transfer NSString *)CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,
                                                                                                 (__bridge CFStringRef)self,
                                                                                                 CFSTR(""),
                                                                                                 kCFStringEncodingUTF8);
}

- (BOOL)matchWithPattern:(NSString *)pattern
{
    NSLog(@"pattern >>>> %@", pattern);
    NSRange match = [self rangeOfString:pattern options:NSRegularExpressionSearch];
    if (match.location != NSNotFound) {
        NSLog(@"<%@> is match <%@>", self, [self substringWithRange:match]);
        return YES;
    }
    return NO;
}

/*
 全角/半角変換
 */
- (NSString *)stringToHalfwidth
{
    return [self stringTransformWithTransform:kCFStringTransformFullwidthHalfwidth reverse:false];
}

- (NSString *)stringToFullwidth
{
    return [self stringTransformWithTransform:kCFStringTransformFullwidthHalfwidth reverse:true];
}

/*
 iOS6のバグ
 http://blog.livedoor.jp/tukuruyo/archives/52181393.html
 */
- (void)dummyTransform
{
    [self stringTransformWithTransform:kCFStringTransformHiraganaKatakana reverse:false];
}

- (NSString *)stringTransformWithTransform:(CFStringRef)transform reverse:(Boolean)reverse
{
    NSMutableString *retStr = [[NSMutableString alloc] initWithString:self];
    CFStringTransform((__bridge CFMutableStringRef)retStr, NULL, transform, reverse);
    return retStr;
}

/*
 全角ハイフン->全角マイナス変換
 */
- (NSString *)safetyUnicodeString
{
    unichar unichars[[self length]];
    for (int i = 0, l = [self length]; i < l; i++) {
        unichar c = [self characterAtIndex:i];
        if (c == 0xff0d) {
            unichars[i] = 0x2212;
        } else {
            unichars[i] = c;
        }
    }
    NSString *text = [NSString stringWithCharacters:unichars length:[self length]];
    /*
    NSLog(@"text >>>>>>> %@", text);
    for (int i = 0; i < [text length]; i++) {
        unichar c = [text characterAtIndex:i];
        NSLog(@"ccccc >>>>>> \\u%04x", c);
    }
     */
    return text;
}

@end