I'm trying to send hexadecimal data via WiFi.
The code is something like this:
NSString *abc = #"0x1b 0x50";
NSData *data = [[[NSData alloc] initWithData:[abc dataUsingEncoding:NSASCIIStringEncoding]]autorelease];
[outputStream write:[data bytes] maxLength:[data length]]];
Instead of sending the hexadecimal data, it's sending it in text format.
I tried with NSUTF8StringEncoding, but it's the same. I'm using it with the NSStream class.
You're not getting what you expect with NSString *abc = #"0x1b 0x50". It's almost the same as having NSString *abc = #"cat dog 123 0x0x0x"; just a bunch of words separated by spaces. So when you create your NSData object, you're just initializing it with a string of characters, not a series of actual numbers.
If you can get your numbers into an NSArray, this question/answer should help you: How to convert NSArray to NSData?
The data that you probably want to send is simply 0x1b50, which is the decimal number 6992 (assuming big-endian), and fits into two bytes. This is not the same as a string (which could contain anything) even if it happens to contain some human-readable representation of those numbers.
I'm assuming you want to send this as binary data, and if so one way would be to simply send a buffer formed by a single UInt16 instead of a string. I'm not very familiar with the relevant APIs, but look to see if you can populate the NSData with an integer, perhaps something like:
UInt16 i = 0x1b50; // Or = 6992
[[NSData alloc] initWithBytes: &i length: sizeof(i)]
[outputStream write: [data bytes] maxLength: [data length]]];
Again, I'm not fluent with Objective C, but this should be the general approach to sending the number 0x1b50 as binary data.
Related
I am trying to display a picture from a byte-array produced by a web service. Printing out a description it looks like this:
("-119",80,78,71,13,10,26,10,0,0,0,13,3 ... )
From the header it is clear that it's a png encoded in signed integers. It is an __NSCFArray having __NSCFNumber elements.
My code in Objective-C (based on much googling):
NSData *data = [NSData dataWithBytes:(const void *)myImageArray length [myImageArray count]];
UIImage *arrayImage = [UIImage imageWithData:data];
I receive a null UIImage pointer.
I also tried to converting it to unsigned NSNumbers first and then passing it to NSData, though perhaps I did not do this correctly. What am I doing wrong?
You cannot simply cast an NSArray of NSNumber into binary data. Both NSArray and NSNumber are objects; they have their own headers and internal structure that is not the same as the original string of bytes. You'll need to convert it byte-by-byte with something along these lines:
NSArray *bytes = #[#1, #2, #3];
NSMutableData *data = [NSMutableData dataWithLength:bytes.count];
for (NSUInteger i = 0; i < bytes.count; i++) {
char value = [bytes[i] charValue];
[data replaceBytesInRange:NSMakeRange(i, 1) withBytes:&value];
}
char is a signed int8_t, which appears to be the kind of data you're working with. It is often used to mean "an ASCII character," but in C it is commonly also used to mean "byte."
I am very new to Objective C and I've been searching Google for a number of hours trying to find a solution.
I have an NSString which looks like
273350/364D4D002A00041EB8F1E0CEF1E0CCF1E0CCF1E0CCF1E0CCF etc etc
which refers to a TIFF image (I guess in some sort of RAW string format), I want to populate an NSImageView with the data.
This is what I've attempted so far:
NSData *picdata = [NSData dataWithBytes:[albumArtStr UTF8String] length:[albumArtStr length]];
NSImage *myPicture = [[NSImage alloc] initWithData:picdata];
[_albumArtCell setImage:myPicture];
Where "albumArtCell" is the NSImageView
That data looks like hex encoded image with a length in front of it, not an unencoded TIFF, which is a tagged binary format. Perhaps you need to strip the number before the slash and decode e rest of the string from hex digits into NSData and then call [[NSImage alloc] initWithData] using that decided data.
You will need to decode it to binary before handing it to NSImage as it only understands the raw binary form of TIFF.
I believe the problem is due to the fact that [albumArtStr length] returns the number of "unicode character", and not number of "bytes".
So your NSData is probably not set-up to be the right size and so doesn't have the right format for a UIImage to be decoded properly.
Try this instead to create a NSData from NSString instance:
NSData* picData = [albumArtStr dataUsingEncoding: NSUTF8StringEncoding];
I have an original NSData type which contains let's say 100 bytes. I want to get 2 other NSData types. The first containing the first 20 bytes of the 100, and the second one containing the other 80.
They should be copied from the original NSData. Sorry if I wasn't so clear, but I'm pretty new with Objective-C.
You can use NSData's -(NSData *)subdataWithRange:(NSRange)range; to do that.
From your example, here is some code :
// original data in myData
NSData *d1 = [myData subdataWithRange:NSMakeRange(0, 20)];
NSData *d2 = [myData subdataWithRange:NSMakeRange(20, 80)];
Of course, the ranges are immediate here, you will probably have to do calculations, to make it work for your actual code.
Swift 3
let subdata1 = data?.subdata(in: 0..<20)
let subdata2 = data?.subdata(in: 20..<80)
Due to this is question is in very top of Google Search I wanna write here an example for swift
NSData *mainData = /*This is you actual Data*/
NSData *fPart = [mainData subdataWithRange:NSMakeRange(0, 20)];
NSData *sPart = [mainData subdataWithRange:NSMakeRange(20, 80)];
Instead 80 you can use some dynamic - like data length
Why does the following code produce the logging at the bottom ?
Here is the anomaly- my second NSLog should print the chrStr but produces nothing, empty, which is verified by this debug command:
(gdb) po chrStr
object returns empty description
However, the third NSString where I re-convert the NSString back to NSData object DOES display the the data, the same value as in the first NSLog, as it should. This would indicate to me that chrStr must have actual contents. But it seems not to be so from the NSLOG or the po command. Why ?
NSString *login;
NSString *pass;
// Purpose: NSString *loginString = [NSString stringWithFormat:#"\000%#\000%#", login, pass];
login = #"Loginname"; // text string1
pass = #"Password"; // text string2
// convert text strings to data objects
NSData *subData1 = [login dataUsingEncoding:NSUTF8StringEncoding];
NSData *subData2 = [pass dataUsingEncoding:NSUTF8StringEncoding];
// embed a NULL into new NSData object
NSMutableData *data = [NSMutableData data];
unsigned char zeroByte = 0;
[data appendBytes:&zeroByte length:1];
// append string1, NULL, string2 to data object
[data appendData:subData1];
[data appendBytes:&zeroByte length:1];
[data appendData:subData2];
NSLog(#"1.NSData: %#", data); // print data object
// create a character string from data object
NSString *chrStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(#"2.NSString: %#", chrStr); // print character string
// create data object from string object
NSData *chrData = [chrStr dataUsingEncoding:NSUTF8StringEncoding];
NSLog(#"3.NSDATA: %#", chrData); // print data object
Produces:
[1071:207] 1.NSData: 004c6f67 696e6e61 6d650050 61737377 6f7264
[1071:207] 2.NSString:
[1071:207] 3.NSDATA: 004c6f67 696e6e61 6d650050 61737377 6f7264
This is a real mystery to me. If chrStr is empty then 3-NSDATA could not display its info, but it does !
What am I trying to accomplish ? Well, check my very first comment line: // purpose:
That line when uncommented produces a warning, even though it actually works, so I was trying to do it another way that allowed me to have a clean compile. If you see a better way to accomplish that objective, I all eyes and ears. But please don't dwell on why that #"\000%#\000%#" string is necessary, start out accepting that it is. Thanks.
In C (and therefore objective-c), a null byte is used to represent the end of a string. When you create the string object, it takes all of the data you have given it without parsing, which is why you can convert it back to data successfully. However, when you display the string, the system reads the string up to the first null byte, which is the first byte. Therefore, the string contains data, but any system functions which read byte by byte instead of using the strings returned length will think it is empty. When you work with non-displayable characters, you should try to use data objects over string objects as often as possible.
I'm storing large unicode characters (0x10000+) as long types which eventually need to be converted to NSStrings. Smaller unicode characters can be created as a unichar, and an NSString can be created using
[NSString stringWithCharacters:(const unichar *)characters length:(NSUInteger)length]
So, I imagine the best way to get an NSString from the unicode long value would be to first get a unichar* from the long value. Any idea on how I might go about doing this?
Is there any reason you are storing the values as longs? For Unicode storage you only need to store the values as UInt32, which would then make it easy to interpret the data as UTF-32 by doing something like this:
int numberOfChars = 3;
UInt32* yourStringBuffer = malloc(sizeof(UInt32) * numberOfChars);
yourStringBuffer[0] = 0x2F8DB; //杞
yourStringBuffer[1] = 0x2318; //⌘
yourStringBuffer[2] = 0x263A; //☺
NSData* stringData = [NSData dataWithBytes:yourStringBuffer length:sizeof(UInt32) * numberOfChars];
//set the encoding according to the current byte order
NSStringEncoding encoding;
if(CFByteOrderGetCurrent() == CFByteOrderBigEndian)
encoding = NSUTF32BigEndianStringEncoding;
else
encoding = NSUTF32LittleEndianStringEncoding;
NSString* string = [[NSString alloc] initWithData:stringData encoding:encoding];
free(yourStringBuffer);
NSLog(#"%#",string);
//output: 杞⌘☺