objective-cで文字コードを自動判別する

NSData+detectEncode.h

#import <Foundation/Foundation.h>

@interface NSData (DetectEncoding)
+(NSStringEncoding) detectEncoding:(NSData *)data;
@end

NSData+detectEncode.m

#import "NSData+DetectEncoding.h"

@implementation NSData (DetectEncoding)

+(NSStringEncoding) detectEncoding:(NSData *)data
{
    NSStringEncoding encoding;
    NSStringEncoding encodings[] = {
        NSUTF8StringEncoding,
        NSNonLossyASCIIStringEncoding,
        NSShiftJISStringEncoding,
        NSJapaneseEUCStringEncoding,
        NSMacOSRomanStringEncoding,
        NSWindowsCP1251StringEncoding,
        NSWindowsCP1252StringEncoding,
        NSWindowsCP1253StringEncoding,
        NSWindowsCP1254StringEncoding,
        NSWindowsCP1250StringEncoding,
        NSISOLatin1StringEncoding,
        NSUnicodeStringEncoding,
        0
    };
    
    int i = 0;
    NSString *try_str;
    
    if (memchr([data bytes], 0x1b, [data length]) != NULL) {
        try_str = [[NSString alloc] initWithData:data encoding:NSISO2022JPStringEncoding];
        if (try_str != nil)
            return NSISO2022JPStringEncoding;
    }
    
    while(encodings[i] != 0){
        try_str = [[NSString alloc] initWithData:data encoding:encodings[i]];
        if (try_str != nil) {
            encoding = encodings[i];
            break;
        }
        i++;
    }
    return encoding;
}

@end