How to efficiently parse 'yyyymmdd' in cs (a c/c++ guy's question)?

  • Thread starter Thread starter Bogdan
  • Start date Start date
B

Bogdan

Hi,

I primarily develop in c/c++ but need to write a relatively simple code in
cs.

I need to parse year, month, and day from strings representing dates as
'yyyymmdd'.

What is the most efficient (speed-wise and memory-wise) way to do that in
cs?

I could use string.IndexOf()/string.Substring()/Int32.Parse() combination
but this seems to create a lot of new string objects.
Is there a better way?

Thanks,
Bogdan
 
Bogdan said:
I primarily develop in c/c++ but need to write a relatively simple code in
cs.

I need to parse year, month, and day from strings representing dates as
'yyyymmdd'.

What is the most efficient (speed-wise and memory-wise) way to do that in
cs?
Click to expand...
You forgot developer-time-wise, which is the most important of all.

DateTime.ParseExact(s, "yyyyMMdd", CultureInfo.InvariantCulture);
I could use string.IndexOf()/string.Substring()/Int32.Parse() combination
but this seems to create a lot of new string objects.
Click to expand...

..NET happens to be very good at handling the creation and near-immediate
discarding of new objects, so that's not necessarily a problem.
Is there a better way?
Click to expand...
In the unlikely case that DateTime isn't good enough (and don't assume this
without testing) you can extract the values without creating substrings, by
simply doing things the hard way (if you're familiar with C, this should
come natural). Slightly obfuscated for your viewing pleasure (disclaimer: I
have no idea what the performance of this is and I'm not testing because I'd
never use it):

if (s.Length != 8) /* fail */;
for (int n = 0; n != 8; ++n) if (s[n] < '0' || s[n] > '8') /* fail */;
int year = s[3] + 10 * (s[2] + 10 * (s[1] + 10 * s[0])) - 53328;
int month = s[5] + 10 * s[4] - 528;
int day = s[7] + 10 * s[6] - 528;
 
Jeroen Mostert said:
You forgot developer-time-wise, which is the most important of all.

DateTime.ParseExact(s, "yyyyMMdd", CultureInfo.InvariantCulture);
Click to expand...

ParseExact() is ideal in my case.
Thanks,
Bogdan
 
Jeroen said:
for (int n = 0; n != 8; ++n) if (s[n] < '0' || s[n] > '8') /* fail */;
Click to expand...

Behold the dangers of premature optimization. This code is casting out nines
when it really shouldn't.
 
* Bogdan wrote, On 6-10-2009 23:26:
ParseExact() is ideal in my case.
Thanks,
Bogdan
Click to expand...

Also look at TryParseExact. It allows you to detect failed parses
without having to catch exceptions. (talking about efficient)
 
Back
Top