Converting int64 to NSData

Question

Hi guys,

I need to convert a long value from int64 to NSData, so I can later run a hash algorithm on it. I perform:

int64_t longNumber = 9000000000000000000L;
NSMutableData *buffer = [NSMutableData dataWithBytes:&longNumber length:sizeof(longNumber)];

NSLog(@"%lld", [buffer bytes]);
NSLog(@"%lld", longNumber);

The resultant console output is like this:

6201314301187184 9000000000000000000

Why is NSData not properly storing the value of the long number? If I run this in a loop, the NSData bytes drift, starting with 620, then 621 and on. Am I outputting the address of the longNumber via [buffer bytes] and not its value?

Answer 1

You have two major issues: first, your number is too large for the long that you are casting it to. Instead of 9000000000000000000L you should have 9000000000000000000LL to indicate a long long constant.

Second, you answered your question correctly, you are printing out an address. Replace your NSLog line with with this line:

NSLog(@"%lld", *((int64_t*)[buffer bytes]));

and you should see the result you expect.