CODEWITHSUNDEEP
iosobjective-cbase64
deKay
deKay

Reputation: 23

correctly convert hex to base64

I'm trying to get the correct base64 string by encoding a hex string. It works when I use converter websited but my App does not.

NSData* sentData = [combinedHexMessage dataUsingEncoding : NSUTF8StringEncoding];
NSLog (@"%@",sentData);
NSData* sentDataBase64 = [sentData base64EncodedDataWithOptions:0];
NSLog(@"%@",[NSString stringWithUTF8String:[sentDataBase64 bytes]]);

This is my code. combinedHexMessage looks like this in NSLog:

ffd8ffe000104a46494600010101006000600000ffdb004300020101020101020 ...

sentData :

66666438 66666530 30303130 34613436 34393436 30303031 30313031 ...

sentDataBase64 :

ZmZkOGZmZTAwMDEwNGE0NjQ5NDYwMDAxMDEwMTAwNjAwMDYwMDAwMGZmZGIwMDQzM ...

But it should look like:

/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAIBAQIBAQICAgICAgICAwUDAwMDAwYEBAMFB ...

Because this is the string I get after I paste my hex string there:

http://tomeko.net/online_tools/hex_to_base64.php?lang=en

What am I doing wrong?

Upvotes: 2

Views: 1582

Answers (1)

Rob
Rob

Reputation: 437917

If you have a hex string that represents an image, you simply want to convert that hex string to a NSData

NSString *hexadecimalString = ...
NSData *data = [hexadecimalString dataFromHexadecimalString];
self.imageView.image = [UIImage imageWithData:data];

Where dataFromHexadecimalString might be defined in a NSString category like so:

@implementation NSString (Hexadecimal)

- (NSData *)dataFromHexadecimalString
{
    // in case the hexadecimal string is from `NSData` description method (or `stringWithFormat`), eliminate
    // any spaces, `<` or `>` characters

    NSString *hexadecimalString = [self stringByReplacingOccurrencesOfString:@"[ <>]" withString:@"" options:NSRegularExpressionSearch range:NSMakeRange(0, [self length])];

    NSMutableData * data = [NSMutableData dataWithCapacity:[hexadecimalString length] / 2];
    for (NSInteger i = 0; i < [hexadecimalString length]; i += 2) {
        NSString *hexChar = [hexadecimalString substringWithRange: NSMakeRange(i, 2)];
        int value;
        sscanf([hexChar cStringUsingEncoding:NSASCIIStringEncoding], "%x", &value);
        uint8_t byte = value;
        [data appendBytes:&byte length:1];
    }

    return data;
}

@end

No base-64 conversion is needed in this process.

Upvotes: 1

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