Encode/Decode struct object - iphone

Question

I am studying this wavefront obj loader example: https://github.com/jlamarche/iOS-OpenGLES-Stuff/tree/master/Wavefront%20OBJ%20Loader
And in order to improve object loading speed - I decided to encode loaded objects as NSValue and then store in Core data. Later, when corresponding object needs to be shown again - I fetch from database necessary nsvalue and unarchieve it.
It's all working, but problem is - it's not as fast I hoped it would be.
One of the reasons - because, in that example are used struct objects.
I was not successful to encode/decode them, so I used NSMutableArray, in which I write all struct data, and later - I iterate through it to put back values to struct object.
For example, there is struct:
typedef struct {
GLfloat x;
GLfloat y;
GLfloat z;
} Vertex3D;
It is then defined:
typedef Vertex3D Vector3D;
But in OpenGLWaveFrontObject class it is used like this:
Vector3D *vertexNormals;
how can I encode/decode struct like this?
I've tried like this:
[coder encodeObject:[NSValue value:&vertexNormals withObjCType:#encode(Vector3D)] forKey:#"vertexNormals"];
or like this:
[coder encodeObject:[NSValue value:&vertexNormals withObjCType:#encode(Vector3D[30])] forKey:#"vertexNormals"];
but its not working - if successfully encoded, then when decoding - values are incorrect.
example, how I put back in array of struct necessary values:
vertices = malloc(sizeof(Vertex3D) * [verticesArray count]);
for(int i = 0; i < [verticesArray count]; i++)
{
vertices[i].x = [[[verticesArray objectAtIndex:i] objectAtIndex:0] floatValue];
vertices[i].y = [[[verticesArray objectAtIndex:i] objectAtIndex:1] floatValue];
vertices[i].z = [[[verticesArray objectAtIndex:i] objectAtIndex:2] floatValue];
}
this works, but I have few more struct arrays and in case arrays are big - this becomes a big issue.
EDIT:
Using Amin Negm-Awad provided answer:
If I simply change NSArchiver to NSKeyedArchiver - it throws error:
[NSKeyedArchiver encodeArrayOfObjCType:count:at:]: unsupported type "{?=fff}]" for array encoding'
When I try:
NSValue *encapsulated = [NSValue valueWithBytes:vertexNormals objCType:#encode(Vertex3D[3])];
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:encapsulated];
[coder encodeObject:data forKey:#"vertexNormals"];
And vertexNormals were created:
vertexNormals = calloc(3, sizeof(Vector3D));
and filled with similar data You provided.
EDIT 2:
Using updated answer which Amin Negm-Awad provided,
I was successfully able to store struct object as NSData and encode it, and after that - decode it. It works!
example, so that it might help some one else too:
//Encode
NSData *verticesData = [NSData dataWithBytes:vertices length:numberOfVertices * sizeof(Vector3D)];
[coder encodeObject:verticesData forKey:#"vertices"];
//Decode
vertices = malloc(sizeof(Vertex3D) * numberOfVertices);
NSData *verticesData = [decoder decodeObjectForKey:#"vertices"];
[verticesData getBytes:vertices length:sizeof(Vertex3D) * numberOfVertices];
where Vertex3D was a struct:
typedef struct {
GLfloat x;
GLfloat y;
GLfloat z;
} Vertex3D;
and used as a struct array (I don't know how it is really called):
Vertex3D *vertices;
Unfortunately I was not able to store texture data. I can encode and decode, but decoded data are always randomly bizarre.
I am declaring it in this way:
GLfloat *textureCoords;
And I Encoded/Decoded in this way:
//Encode
NSData *textureCoordsData = [NSData dataWithBytes:textureCoords length:valuesPerCoord * numberOfVertices];
[coder encodeObject:textureCoordsData forKey:#"textureCoords"];
//Decode
textureCoords = malloc(sizeof(GLfloat) * valuesPerCoord * numberOfVertices);
NSData *textureCoordsData = [decoder decodeObjectForKey:#"textureCoords"];
[textureCoordsData getBytes:textureCoords length:valuesPerCoord * numberOfVertices];
What could be the problem?

Answer 1

First of all: If the array has variable length, it is simply not possible to use NSValue. This is documented:
The type you specify must be of constant length. You cannot store C
strings, variable-length arrays and structures, and other data types
of indeterminate length in an NSValue—you should use NSString or
NSData objects for these types.
So you should really take into account to use NSData instead.
But, if you want to use NSValue (because you have a constant-length array):
Both of your approaches has an extra indirection. The first one has the wrong type, too. What should work:
// Create some data
Vertex3D *cArray = malloc(30 * sizeof(Vertex3D));
NSInteger i;
for (i=0; i<30; i++)
{
cArray[i].x = i;
cArray[i].y = 9811;
cArray[i].z = 29-i;
}
NSLog(#"%p", cArray);
// Encapsulate that in a value
// Have a look at the parameters
NSValue *encapsulated = [NSValue valueWithBytes:cArray objCType:#encode(Vertex3D[30])];
// Put it through a coder and store the coded data on disk
NSData *data = [NSArchiver archivedDataWithRootObject:encapsulated];
[data writeToFile:[#"~/Desktop/valueTest" stringByExpandingTildeInPath] atomically:YES];
// Out is done here
// from disk
data = [NSData dataWithContentsOfFile:[#"~/Desktop/valueTest" stringByExpandingTildeInPath]];
encapsulated = [NSUnarchiver unarchiveObjectWithData:data];
Vertex3D *cArray2 = malloc(30 * sizeof(Vertex3D));
[encapsulated getValue:cArray2];
for (i=0; i<30; i++)
{
NSLog(#"%f %f %f", cArray[i].x, cArray[i].y, cArray[i].z);
}
NSLog(#"%p", cArray2);
This works in my test code
Update because of the problem with keyed achieving:
To store the c array in an instance of NSData instead of an instance of NSValue do this instead
After
NSLog(#"%p", cArray);
change the code to
// Convert to an NSData instance
NSData *data = [NSData dataWithBytes:cArray length:lengthInBytes];
[data writeToFile:[#"~/Desktop/valueTest" stringByExpandingTildeInPath] atomically:YES];
// Out is done here
// from disk
data = [NSData dataWithContentsOfFile:[#"~/Desktop/valueTest" stringByExpandingTildeInPath]];
Vertex3D *cArray2 = malloc(lengthInBytes);
[data getBytes:cArray2 length:lengthInBytes];
until
for (i=0; i<30; i++)