I have a NSData item that is holding a bunch of ints. How do I go about getting them out and into an NSArray?
The memory structure in the NSData is 32-bit int in little-endian order, one right after the other.
Sorry for the basic question, but still learning the obj-c way of doing things :)
You can use the functions defined in OSByteOrder.h to deal with endianness. Aside from that quirk, this is really just a matter of grabbing the byte buffer and iterating over it.
// returns an NSArray containing NSNumbers from an NSData
// the NSData contains a series of 32-bit little-endian ints
NSArray *arrayFromData(NSData *data) {
void *bytes = [data bytes];
NSMutableArray *ary = [NSMutableArray array];
for (NSUInteger i = 0; i < [data length]; i += sizeof(int32_t)) {
int32_t elem = OSReadLittleInt32(bytes, i);
[ary addObject:[NSNumber numberWithInt:elem]];
}
return ary;
}
Sounds like there are cleaner ways to do what you're trying to do, but this should work:
NSData *data = ...; // Initialized earlier
int *values = [data bytes], cnt = [data length]/sizeof(int);
for (int i = 0; i < cnt; ++i)
NSLog(#"%d\n", values[i]);
This answer is very similar to other answers above, but I found it instructive to play with casting the NSData bytes back to an int32_t[] array. This code works correctly on a little-endian processor (x64 in my case) but would be silently wrong on big-endian (PPC) because the byte representation would be big-endian.
int32_t raw_data[] = {0,1,2,3,4,5,6,7,8,9,10};
printf("raw_data has %d elements\n", sizeof(raw_data)/sizeof(*raw_data));
NSData *data = [NSData dataWithBytes:(void*)raw_data length:sizeof(raw_data)];
printf("data has %d bytes\n", [data length]);
int32_t *int_data_out = (int32_t*) [data bytes];
for (int i=0; i<[data length]/4; ++i)
printf("int %d = %d\n", i, int_data_out[i]);
[data release];
One possible solution below.
To take endianness into account, look up Core Endian Reference in the XCode doc set (you probably would use EndianS32_LtoN (32 bit litte endian to native endianness)).
int mem[]= {0x01, 0x02, 0x03, 0x04, 0xff};
NSData * data = [NSData dataWithBytes:mem length:sizeof(mem)*sizeof(int)];
NSMutableArray * ar = [NSMutableArray arrayWithCapacity:10];
/* read ints out of the data and add them to the array, one at a time */
int idx=0;
for(;idx<[data length]/sizeof(int);idx+=sizeof(int))
[ar addObject:[NSNumber numberWithInt:*(int *)([data bytes] + idx)]];
NSLog(#"Array:%#", ar);
Related
I have a ASCII file which I want to read byte by byte into a Byte buffer. I am clueless and confused between many aspects. Can anyone guide me with the correct way to do it?
Any help is appreciated.
I finaly got the answer here. So what I did is,
NSMutableString *bundlePath = [NSMutableString stringWithString:
[[NSBundle mainBundle]pathForResource:#"excercise1" ofType:nil]];
NSData *myData = [NSData dataWithContentsOfFile:bundlePath];
uint8_t * bytePtr = (uint8_t * )[myData bytes];
NSInteger totalData = [myData length] / sizeof(uint8_t);
NSLog(#"Data byte chunk: ");
for (int i = 0 ; i < totalData; i ++)
{
NSLog(#" %x", bytePtr[i]);
}
and it worked as I wanted it to be. I got the bytes in an array.
How would I set a byte in an NSMutableData object?
I tried the following:
-(void)setFirstValue:(Byte)v{
[mValues mutableBytes][0] = v;
}
But that makes the compiler cry out loud...
But that makes the compiler cry out loud...
That is because mutableBytes* returns void*. Cast it to char* to fix the problem:
((char*)[mValues mutableBytes])[0] = v;
You could also use replaceBytesInRange:withBytes:
char buf[1];
buf[0] = v;
[mValues replaceBytesInRange:NSMakeRange(0, 1) withBytes:buf];
I cast it to an array
NSMutableData * rawData = [[NSMutableData alloc] initWithData:data];
NSMutableArray * networkBuffer = [[NSMutableArray alloc]init];
const uint8_t *bytes = [self.rawData bytes];
//cycle through data and place it in the network buffer
for (int i =0; i < [data length]; i++)
{
[networkBuffer addObject:[NSString stringWithFormat:#"%02X", bytes[i]]];
}
then of course you can just adjust objects in your networkBuffer (which is an nsmutablearray)
How can I iterate through [NSData bytes] one by one and append them to an NSMutableString or print them using NSLog()?
Rather than appending bytes to a mutable string, create a string using the data:
// Be sure to use the right encoding:
NSString *result = [[NSString alloc] initWithData:myData encoding:NSUTF8StringEncoding];
If you really want to loop through the bytes:
NSMutableString *result = [NSMutableString string];
const char *bytes = [myData bytes];
for (int i = 0; i < [myData length]; i++)
{
[result appendFormat:#"%02hhx", (unsigned char)bytes[i]];
}
Update! Since iOS 7, there's a new, preferred way to iterate through all of the bytes in an NSData object.
Because an NSData can now be composed of multiple disjoint byte array chunks under the hood, calling [NSData bytes] can sometimes be memory-inefficient, because it needs to flatten all of the underlying chunks into a single byte array for the caller.
To avoid this behavior, it's better to enumerate bytes using the enumerateByteRangesUsingBlock: method of NSData, which will return ranges of the existing underlying chunks, which you can access directly without needing to generate any new array structures. Of course, you'll need to be careful not to go poking around inappropriately in the provided C-style array.
NSMutableString* resultAsHexBytes = [NSMutableString string];
[data enumerateByteRangesUsingBlock:^(const void *bytes,
NSRange byteRange,
BOOL *stop) {
//To print raw byte values as hex
for (NSUInteger i = 0; i < byteRange.length; ++i) {
[resultAsHexBytes appendFormat:#"%02x", ((uint8_t*)bytes)[i]];
}
}];
ex:
NSData *data = [NSData dataWithContentsOfFile:filePath];
int len = [data length];
if len = 10000,
i hope i can convert 1000 to a NSData look like
char hoperesult[] = {0x10, 0x27, 0x00, 0x00}
and hoperesult[] must always 4 Bytes
So you want the length in 4 little-endian bytes, correct? I think this will do it:
unsigned int len = [data length];
uint32_t little = (uint32_t)NSSwapHostIntToLittle(len);
NSData *byteData = [NSData dataWithBytes:&little length:4];
(Note that most network protocols use big-endian, but you showed little-endian so that's what this does.)
I'm not 100% sure what you mean here, but I think you are attempting to fill hoperesult with the values found in the file at 'filePath'.
struct _hoperesult {
char data[4];
} *hoperesult;
NSData *data = [NSData dataWithContentsOfFile:filePath];
NSUInteger len = [data length];
NSRange offset;
offset.location = 0;
offset.length = sizeof(_hoperesult);
NSData *hoperesultData;
while( (offset.location + offset.length) < len ) {
hoperesultData = [data subdataWithRange:offset];
// the equivalent of your char hoperesult[] content...
hoperesult = [hoperesultData bytes]
}
An instance of NSData can return a pointer to the actual bytes of data using the "bytes" method. It returns a (const void *). You could in theory simply cast [data bytes] to a char * and use the offset directly; or you can do like in the above code and return smaller chucks of NSData.
Hope that helps!
I have this function:
void myFunc(NSString* data) {
NSMutableArray *instrs = [[NSMutableArray alloc] initWithCapacity:[data length]];
for (int i=0; i < [data length]; i++) {
unichar c = [data characterAtIndex:i];
[instrs addObject:c];
}
NSEnumerator *e = [instrs objectEnumerator];
id inst;
while (inst = [e nextObject]) {
NSLog("%i\n", inst);
}
}
I think it fails at [instrs addObject:c]. It's purpose is to iterate through the hexadecimal numbers of an NSString. What causes this code to fail?
A unichar is not an object; it's an integer type.
NSMutableArray can only hold objects.
If you really want to put it into an NSMutableArray, you could wrap the integer value in an NSNumber object: [instrs addObject:[NSNumber numberWithInt:c]];
But, what's the point of stuffing the values into an array in the first place? You know how to iterate through the string and get the characters, why put them into an array just to iterate through them again?
Also note that:
the "%i" NSLog format expects an integer; you can't pass it an object
for hexadecimal output, you want "%x", not "%i"
If the function is only meant to display the characters as hexadecimal values, you could use:
void myFunc(NSString* data)
{
NSUInteger len = [data length];
unichar *buffer = calloc(len, sizeof(unichar));
if (!buffer) return;
[data getCharacters:buffer range:NSMakeRange(0, len)];
for (NSUInteger i = 0; i < len; i++)
NSLog(#"%04x", (unsigned) buffer[i]);
free(buffer);
}
This is just a little bit more efficient than your approach (also, in your approach you never release the instrs array, so it will leak in a non-garbage-collected environment).
If the string contains hexadecimal numbers, then you will want to repeatedly use an NSScanner's scanHexInt: method until it returns NO.
void myFunc(NSString* data)
{
NSScanner *scanner = [[NSScanner alloc] initWithString:data];
unsigned number;
while ([scanner scanHexInt:&number])
NSLog(#"%u", number);
[scanner release];
}