ios socket outputstream bytes

Question

I find these code on the website,and rewrite it into my current code ,I can successfully connect to the server side.But I still had some problems:

outputStream:

According to the code on the website, I can normally send string

- (IBAction)sendCmd:(id)sender
{
    NSString *response  = @"Hello World!";
    NSData *data = [[NSData alloc] initWithData:[response dataUsingEncoding:NSASCIIStringEncoding]];
    [outputStream write:[data bytes] maxLength:[data length]];
}

But I want to send bytes,(e.g 0x80,0x10,0x20...etc.) Android syntax is:

         byte[] buf=new byte[10];
                buf[0]=(byte) 0x80;  
                buf[1]=(byte) 0x10; 
                buf[2]=(byte) 0x20;

But replaced ios,I don't know how to do? Give me some advice or website,grateful.

What is the problem? Use an OutputStream too and its write() method. — greenapps, Apr 10 '15 at 15:50
`-[outputStream write: maxLength:]` takes bytes. That's why you have to do the whole encoding to `NSData` and calling `[data bytes]` and `[data length]` thing when you have a string. If you already have bytes, just send them. — abarnert, Apr 11 '15 at 00:33
I'm sorry I may have made a fatal mistake ...what I wanna show is to convey a HEX, — Shane Jhan, Apr 11 '15 at 15:20
I have no idea what "convey a HEX" means. If you mean you want to send the string "0x80,0x10,0x12" or "801012" or something like that, rather than what your Android code sends, then that's fine—it's just a string, which you can send the same as any other string (using your original code). Again, to make this clear: your Android code does _not_ send hex, it just sends the bytes as bytes. — abarnert, Apr 13 '15 at 02:47
I've rolled back the question to the original version. If you want to ask a new question, after having gotten an answer to your original question, just create a new question. (You can paste links between the two questions—click the "share" button to get a nice link—if you need to.) Otherwise, your question and any existing answers will never be useful to anyone else. — abarnert, Apr 13 '15 at 02:49

abarnert · Accepted Answer · 2015-04-11T00:47:28.777

When you say "I have bytes", that presumably means either:

You have an NSData or similar type holding the bytes. You can see how to get the bytes and length for that from your existing example—just skip the part where you encode the NSString to an NSData, because you already have an NSData.
You have a raw C buffer (via a void * or char * or unsigned char * or similar) and a length. That's exactly what -[NSOutputStream write: maxLength:] wants from you; where your example passes [data bytes] and [data length], just pass your pointer (possibly with a cast) and length values.

For example:

const char msg[] = "\x80\x10\x20";
const NSUInteger msglen = sizeof(msg) / sizeof(*msg);
[outputStream write:(const uint8_t *)msg maxLength:msglen];

If you really want an exact ObjC equivalent of your Android code for some bizarre reason, it would look something like this:

NSMutableData *data = [NSMutableData dataWithLength:10];
uint8_t *buf = (uint8_t *)[data mutableBytes];
buf[0]=(uint8_t)0x80;
buf[1]=(uint8_t)0x10;
buf[2]=(uint8_t)0x20;
[outputStream write:buf maxLength:3]; // or is that 10?

I'm not sure why you're creating a 10-byte buffer and only filling in 3 bytes, but +dataWithLength does the same thing as Android Java and leaves the other 7 slots filled with 0's, if that's what you want.

(You can also just use calloc and skip all the ObjC stuff if you want, but then you have to deal with checking for NULL, calling free at the end even if there was an error somewhere, etc., because C isn't Java…)

Thanks for your answers, but I still need to solve some problems — Shane Jhan, Apr 12 '15 at 14:49
@ShaneJhan: OK, then go solve them, and if you have a new question while doing so, come back to StackOverflow and post a new question. Don't try to edit this question into a new question. — abarnert, Apr 13 '15 at 02:47

ios socket outputstream bytes

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