accessor-Objective C - objective-c

Question

I am new to Objective C.
I need to know how to access the instance variable using the accessors.
I could able to access integer variables but not the character variable which i have declared here.
Please correct if there is any wrong in this code below.
#define SIZE = 4096
#interface data : NSObject
{
unsigned char id[SIZE];
}
#property(readwrite)unsigned char id[SIZE];
#end
#implementation data
#synthesize unsigned char id[SIZE];
#end
main.m
someClass* classPointer = [[someClass alloc]init];
data* dt = [[data alloc]init];
[classPointer createMessage:data.id];

Answer 1

Why not use an instance of NSString or NSData for the instance variable instead of an array of chars? For example:
#interface Foo2 : NSObject
{
NSString *_dataId;
}
#property (nonatomic, retain) NSString *dataId;
#end
#implementation Foo2
#synthesize dataId = _dataId;
#end
Otherwise you'd have to do something along these lines:
#define DATA_ID_SIZE 4096
#interface Foo : NSObject
{
char _dataID[DATA_ID_SIZE];
}
#property (nonatomic, assign) const char *dataID;
#end
#implementation Foo
// Returns a copy of the internal array of chars.
- (const char *)dataID
{
size_t length = strlen(_dataID);
// Dynamically allocate an array of chars to return.
char *buf = malloc(length);
// Copy the values from the internal array.
memcpy(buf, _dataID, length);
return buf;
}
- (void)setDataID:(const char *)dataID
{
// Copy provided chars into the internal array.
memcpy(_dataID, dataID, DATA_ID_SIZE);
// To be on the safe side, copy null character to the last element.
_dataID[DATA_ID_SIZE - 1] = '\0';
}
By the way, id is a data type in Objective-C, so it's best not to use it as a variable name.

Answer 2

You haven't set id anywhere, so it's just going to be nil.
Also on a side note, you must release the objects that you alloc init.

Answer 3

How do you want to manage the memory is the sample above? char c[size] is an array and it will take sizeof(char) * size bytes as the class member, but the property declared in the same manner will read/write pointer, not the data! I suggest you to use NSData* (or NSMutableData) instead of C-array, it's the preferred way for Obj-C.