Converting a hexadecimal string into binary in Objective-C

Question

What's an equivalent of the PHP function pack:

pack('H*', '01234567989abcdef' );

in Objective-C?

Possible duplicate: stackoverflow.com/q/7194528/465378

Alexis King
– Alexis King

2012-01-21 04:32:56 +00:00
Commented Jan 21, 2012 at 4:32 — Alexis King
– Alexis King, Commented Jan 21, 2012 at 4:32
possible duplicate: How to convert hex to binary

jscs
– jscs

2012-01-21 19:58:49 +00:00
Commented Jan 21, 2012 at 19:58 — jscs
– jscs, Commented Jan 21, 2012 at 19:58

iccir · Accepted Answer · 2015-09-18 00:08:40Z

2

Assuming that you want the results as an NSData, you can use a function similar to this:

NSData *CreateDataWithHexString(NSString *inputString)
{
    NSUInteger inLength = [inputString length];

    unichar *inCharacters = alloca(sizeof(unichar) * inLength);
    [inputString getCharacters:inCharacters range:NSMakeRange(0, inLength)];

    UInt8 *outBytes = malloc(sizeof(UInt8) * ((inLength / 2) + 1));

    NSInteger i, o = 0;
    UInt8 outByte = 0;
    for (i = 0; i < inLength; i++) {
        UInt8 c = inCharacters[i];
        SInt8 value = -1;

        if      (c >= '0' && c <= '9') value =      (c - '0');
        else if (c >= 'A' && c <= 'F') value = 10 + (c - 'A');
        else if (c >= 'a' && c <= 'f') value = 10 + (c - 'a');            

        if (value >= 0) {
            if (i % 2 == 1) {
                outBytes[o++] = (outByte << 4) | value;
                outByte = 0;
            } else if (i == (inLength - 1)) {
                outBytes[o++] = value << 4;
            } else {
                outByte = value;
            }

        } else {
            if (o != 0) break;
        }        
    }

    return [[NSData alloc] initWithBytesNoCopy:outBytes length:o freeWhenDone:YES];
}

edited Sep 18, 2015 at 0:08

answered Jan 21, 2012 at 4:32

iccir

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8 Comments

Kamchatka Over a year ago

Thanks this works. There is nothing doing that in the Cocoa libraries already?

Kamchatka Over a year ago

Also it looks like you're leaking inCharacters

iccir Over a year ago

inCharacters is allocated using alloca, which allocates space on the stack rather than the heap. If you are dealing with large strings and don't feel comfortable advancing the stack pointer that far, you probably want to change inCharacters to a malloc() and free() it before the return.

iccir Over a year ago

Oops, didn't see your first reply. It depends on your use case - If the hex value is short enough that you can store it an unsigned int or unsigned long long, there is -[NSScanner scanHexLongLong:]. If you need to do additional extraction, you could use the wscanf() family on -[NSString characters]

DrMickeyLauer Over a year ago

This will not work for hex strings with odd-numbers. You need to change the else clause to { outByte = value; if ( i == inLength - 1 ) // this is going to be the last iteration { outBytes[o++] = outByte << 4; } } otherwise you're missing data.

|

NSResponder · Accepted Answer · 2012-01-21 09:09:28Z

1

See the -scanHex... methods of NSScanner.

answered Jan 21, 2012 at 9:09

NSResponder

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