Struct to NSData between Mac and iOS - ios

Question

I have been working on this problem for a while, I have an app running on the mac, it has co-ordinate data stored in a struct like this:
struct xyz {
float x;
float y;
float z;
};
struct xy {
float x;
float y;
};
struct object {
struct xyz *myXYZ;
struct xy *myXY;
};
This all works as expected, then I add the struct into NSData like so:
struct object anInitialTestStruct;
NSMutableData *myTestDataOut = [NSMutableData dataWithBytes:&anInitialTestStruct length:64 freeWhenDone:NO];
BOOL good = [myTestDataOut writeToFile:[NSString stringWithFormat:#"%#/filename.dat", docsDirectory] atomically:YES];
This works as expected, I get a file and looks like there is data in it (for reference I have used pointers and malloc for the anInitialTestStruct but still don't get the desired result)
Now on the iphone, I copy the file into the project, and do this:
NSString *filePath = [[NSBundle mainBundle] pathForResource:#"filename" ofType:#"dat"];
NSData *myVecNSData = [[NSData alloc] initWithContentsOfFile:filePath options:NSDataReadingUncached error:&error];
if ( error ) {
NSLog(#"%#", error);
}
I don't get the correct data back. Interestingly if I run the initWithContents method on the mac and read the file in there it appears to be ok.
So I'm thinking there is something different on the iphone / mac way it deals with the filesystem.... I've tried encoding the data using NSKeyedArchiver, but I get an exception stating "incomprehensible archive....."

Answer 1

For case of your "object" structure you have to store "xy" and "xyz" structures separately, for example in a dictionary:
struct object anInitialTestStruct;
NSDictionary *structureDataAsDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
[NSMutableData dataWithBytes:anInitialTestStruct.myXY length:sizeof(xy)], #"xy key",
[NSMutableData dataWithBytes:anInitialTestStruct.myXYZ length:sizeof(xyz)], #"xyz key",
nil];
NSData *myTestDataOut = [NSKeyedArchiver archivedDataWithRootObject:structureDataAsDictionary];
BOOL good = [myTestDataOut writeToFile:[NSString stringWithFormat:#"%#/filename.dat", docsDirectory] atomically:YES];
and decoding is something like this:
struct object anInitialTestStruct;
NSString *filePath = [[NSBundle mainBundle] pathForResource:#"filename" ofType:#"dat"];
NSData *myVecNSData = [[NSData alloc] initWithContentsOfFile:filePath options:NSDataReadingUncached error:&error];
if ( error ) {
NSLog(#"%#", error);
}
// retrieving dictionary from NSData
NSDictionary *structureDataAsDictionary = [NSKeyedUnarchiver unarchiveObjectWithData:myVecNSData];
// allocating memory for myXY and myXYZ fields
anInitialTestStruct.myXY = (xy*)malloc(sizeof(xy));
if (anInitialTestStruct.myXY == NULL) {
// error handling
}
anInitialTestStruct.myXYZ = (xyz*)malloc(sizeof(xyz));
if (anInitialTestStruct.myXYZ == NULL) {
// error handling
}
// filling myXY and myXYZ fields with read data
[[structureDataAsDictionary objectForKey:#"xy key"] getBytes:anInitialTestStruct.myXY];
[[structureDataAsDictionary objectForKey:#"xyz key"] getBytes:anInitialTestStruct.myXYZ];

Answer 2

You might have truble encoding your pointers see here
"Pointers
You can’t encode a pointer and get back something useful at decode time. You have to encode the information to which the pointer is pointing. This is true in non-keyed coding as well. ..."