How to use assign instead of memcpy - objective-c

Question

I learned memcpy here
The demo shows memcpy is much like assign
How to use assign instead of memcpy
- (uint64_t)parseHeader:(NSData *)data {
uint64_t headerLength = 0;
memcpy(&headerLength, data.bytes, sizeof(uint64_t));
// set a breakpoint
return headerLength;
}
I suppose that headerLength should equal to (uint64_t)(data.bytes)
And I p at that breakpoint
here is the result:
(lldb) p headerLength
(uint64_t) $0 = 318
(lldb) p data.bytes
(const void *) $1 = 0x00006000000050e0
(lldb) p (uint64_t)(data.bytes)
(uint64_t) $2 = 105553116287200
So how to understand memcpy in this context?
I want to use more OOP to get rid of memcpy
More Code:
I encounter this when learning GCDAsyncSocket
The above is the receiving data part.
The sending data part:
typedef NS_ENUM(NSInteger, PacketType){
PacketTypeUnknown = -1,
PacketTypeDidAddDisc,
PacketTypeStartNewGame
};
typedef NS_ENUM(NSInteger, PacketAction){
PacketActionUnknown = -1
};
#interface PacketH: NSObject<NSSecureCoding>
#property (strong, nonatomic) id data;
#property (assign, nonatomic) PacketType type;
#property (assign, nonatomic) PacketAction action;
#end
- (void)sendPacket:(PacketH *)packet {
// Encode Packet Data
NSError * error;
NSData * encoded = [NSKeyedArchiver archivedDataWithRootObject:packet requiringSecureCoding:NO error: &error];
// Initialize Buffer
NSMutableData *buffer = [[NSMutableData alloc] init];
// buffer = header + packet
// Fill Buffer
uint64_t headerLength = encoded.length;
[buffer appendBytes:&headerLength length:sizeof(uint64_t)];
[buffer appendBytes: encoded.bytes length: headerLength];
// Write Buffer
[self.socket writeData:buffer withTimeout:-1.0 tag:0];
}

Answer 1

Thanks #user3386109,
getBytes:length: method of NSData , is much like memcpy
- (uint64_t)parseHeader:(NSData *)data {
NSInteger headerLength = 0;
[data getBytes: &headerLength length:sizeof(uint64_t)];
return headerLength;
}