byte array in ios

Question

I'm trying to convert this Javascript code:

self.userSerialEvent = function (join, value, tokens) {
        var type = join.charCodeAt(0);
        var rawJoin = parseInt(join.substr(1)) - 1;
        var rawValue = parseInt(value);
        self.SJValues[join] = value;

        var payload = "\x00\x00" + String.fromCharCode(value.length + 2) + "\x12" + String.fromCharCode(rawJoin) + value;
        self.sendMsg("\x05\x00" + String.fromCharCode(payload.length) + payload);
    };

to objective c code for an ipad app. However I cannot figure out how to properly form this If I do a char array I cannot have variable length (which will happen when the value is added to the array). And when I try to use NSMutableArray I cant insert bytes, plus my network send operation takes an NSData and I cannot convert a NSMutableArray to data. I have also tried NSString but when I do:

NSString * payload = [NSString stringWithFormat:@"0000%d12%d%@",value.length+2,rawJoin,[value dataUsingEncoding:NSASCIIStringEncoding]];

I get the < > around the data in the string. I have tried to create a character set and remove "<>" from the string but that only removed the end one (leaving the beginning < there)

My question is this: How can I form an array of bytes, that is of variable length and able to convert that array to NSData

rob mayoff · Accepted Answer · 2012-01-27 16:22:53Z

6

Sounds like you are looking for NSMutableData.

NSMutableData *payload = [[NSMutableData alloc] init];
[payload appendBytes:"\000\000" length:2];
uint8_t length = value.length + 2;
[payload appendBytes:&length length:1];
[payload appendBytes:"\022" length:1];
// etc.

answered Jan 27, 2012 at 16:22

rob mayoff

387k69 gold badges842 silver badges887 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

owen gerig Over a year ago

awesome thank you, i should have figured nsmutabledata. thanks again. (5mins till i can accept)

owen gerig Over a year ago

i have been doing 0x01 for hex bytes, but for this i will use /001 ?

Tommy Over a year ago

@owengerig 0x01 is the integer literal with that hex value. If you put it in a string then it'll just be the character stream of a 0 followed by an x followed by a 0, et seq. C strings (as used here) allow byte values to be inserted directly into the character sequence with either \ooo where each o is an octal digit or \xhh where h is a hexadecimal digit (which appears to be what you're doing in the Java original?)

rob mayoff Over a year ago

I wasn't sure if "\x01" was valid in current Objective-C (it was not part of the language when I learned it), but it is indeed valid now. Octal escapes have always been valid.

rob mayoff Over a year ago

Hex A = octal 12 = decimal 10.

Collectives™ on Stack Overflow

byte array in ios

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related