Convert MongoDB BSON ObjectId (oid) to generated time in Objective-C?

Question

I've found this:

function: http://github.com/timburks/NuMongoDB/blob/master/src/bson.c#L128 bytes: http://github.com/timburks/NuMongoDB/blob/master/src/platform_hacks.h#L55 struct: http://github.com/timburks/NuMongoDB/blob/master/src/bson.h#L70

But how exactly would I use this for my iPhone app that gets the oid as a string from the server and want to extract the created_at timestamp? This is what I have so far. It's an Objective-C method, but can I put c code in my Objective-c .m file?

- timeFromBsonOid:(NSString *)oid {
    time_t out;
    memcpy(&out, oid, 4);
    return out;
}

Matt

Answer 1

You can convert the oid string to NSDate like this:

NSString *asd = @"4c8f695bdaf9856dbe000008";
long result;
BOOL success = [[NSScanner scannerWithString:[asd substringToIndex:8]] scanHexLongLong:&result];
NSDate *date = [[NSDate alloc] initWithTimeIntervalSince1970:result];

Answer 2

Kossi's answer's a bit out of date. Make sure to use unsigned long long instead as otherwise you may notice odd behavior and crashes on 32bit and 64bit devices.

NSString *asd = @"4c8f695bdaf9856dbe000008";
unsigned long long result;
BOOL success = [[NSScanner scannerWithString:[asd substringToIndex:8]] scanHexLongLong:&result];
NSDate *date = [[NSDate alloc] initWithTimeIntervalSince1970:result];