How do you append a NSInteger to NSMutableData. Something allong the lines of...
NSMutableData *myData = [[NSMutableData alloc] init];
NSInteger myInteger = 42;
[myData appendBytes:myInteger length:sizeof(myInteger)];
So that 0x0000002A will get appended to myData.
Any help appreciated.
Pass the address of the integer, not the integer itself. appendBytes:length: expects a pointer to a data buffer and the size of the data buffer. In this case, the "data buffer" is the integer.
[myData appendBytes:&myInteger length:sizeof(myInteger)];
Keep in mind, though, that this will use your computer's endianness to encode it. If you plan on writing the data to a file or sending it across the network, you should use a known endianness instead. For example, to convert from host (your machine) to network endianness, use htonl():
uint32_t theInt = htonl((uint32_t)myInteger);
[myData appendBytes:&theInt length:sizeof(theInt)];
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'm new in the area of Objective-C.
My question is, how can I Send a byte format like b70f using NSData?
So, basically I have to make a variable first with the value of b70f and then write it to the peripheral.
[peripheral writeValue:[NSData dataWithBytes:&value length:1] forCharacteristic:characteristic type:CBCharacteristicWriteWithResponse];
How can I do this?
Any help would be appreciated.
Assuming that b70f is a 16-bit value, something like this should work...
uint16_t value = 0xb70f;
NSData *data = [NSData dataWithBytes:&value length:2];
This takes advantage that an "array" of two bytes fits into a single 16-bit integer.
If the bytes are in the wrong order, wrap the assignment with OSSwapInt16().
uint16_t value = OSSwapInt16(0xb70f);
i got the following char array in Objective-C (Xcode):
char *incomeMessage;
NSString *str = [[NSString alloc] initWithBytes:data.bytes length:data.length encoding:NSUTF8StringEncoding];
incomeMessage = [str UTF8String];
NSLog(#"%c", incomeMessage[0]);
NSLog(#"%c", incomeMessage[1]);
NSLog(#"%c", incomeMessage[2]);
NSLog(#"%c", incomeMessage[3]);
NSLog(#"%c", incomeMessage[4]);
NSLog(#"%c", incomeMessage[5]);
For example I get some results like this in console:
"3
2
6
1
8
4"
Now i want to replace the char in incomeMessage[2] by 4:
incomeMessage[2] = '4';
But then it gives me the error:
EXC_BAD_ACCESS
Do you have an idea, how to solve the problem?
According to the reference documentation, UTF8String returns a read-only (const char*) reference to the string data.
The reference material goes on to note:
This C string is a pointer to a structure inside the string object,
which may have a lifetime shorter than the string object and will
certainly not have a longer lifetime. Therefore, you should copy the C
string if it needs to be stored outside of the memory context in which
you use this property.
So I'd suggest following their advice and creating a copy of the array and then performing your modifications against that.
For example: http://ideone.com/mhjwZW
You might have better luck with something like:
NSString* str = [[NSString alloc] initWithBytes:data.bytes length:data.length encoding:NSUTF8StringEncoding];
char* incomeMessage = malloc([str lengthOfBytesUsingEncoding:NSUTF8StringEncoding] + 1);
strcpy(incomeMessage, [str UTF8String]);
//now you can change things
incomeMessage[2] = '4';
//do this when you're done
free(incomeMessage);
Although, is there any particular reason why you want to use a C-string/character array as opposed to an NSMutableString? I think you might find replaceCharactersInRange:withString: a better approach generally. See also: stringByReplacingCharactersInRange:withString:.
i got the following char array in Objective-C (Xcode)
You don't, you know. All you have is a pointer. You have not set aside any actual memory; there is no array there.
incomeMessage = [str UTF8String];
All you've done in that line is repoint the pointer incomeMessage at your string's UTF8String. A string's UTF8String is immutable. Note this passage in the docs:
you should copy the C string if it needs to be stored outside of the memory context in which you use this property.
So basically, if you want to write into an array of char, your first task should be to make an array of char.
I am trying to send the following hex to NSOutputstream 0x0000000e000000010000001000003014
I'm able to send hex that is 8 bit with the following code:
long myhex = 0x0000000e00000001;
NSData *data = [[NSData alloc] initWithBytes:&myhex length: sizeof(myhex)];
[outputStream write:[data bytes] maxLength:[data length]];
The problem is when I try this:
long myhex = 0x0000000e000000010000001000003014;
it says "integer constant is too long for its type"
I cant seem to figure out what type of integer will except this hex value.
Instead of trying to find an integer type long enough, you should probably just create an array of bytes and send that. Not only will you eventually be unable to find a type long enough for the data you wish to send, but there are also differences in the order of bytes in integers on different platforms.
So, to send arbitrarily long data in any order, use an array of bytes (unsigned char, or, preferably, uint8_t from stdint.h), e.g.:
uint8_t dataBytes[] = { 0x00, … , 0x0e, … 0x30, 0x14 };
NSData *data = [[NSData alloc] initWithBytes:dataBytes length:sizeof(dataBytes)];
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.