C++ RSS C++ RSS

check the length of a hex number?

Please support our C++ advertiser: Intel Parallel Studio Home
Reply

•
•
Join Date: Jan 2008
Posts: 401
Reputation: CoolGamer48 is on a distinguished road 
Solved Threads: 40
CoolGamer48's Avatar
CoolGamer48 CoolGamer48 is offline Offline
Posting Pro in Training

check the length of a hex number?

 
0
  #1
Aug 17th, 2008
Hey

I'm writing a color class, and I want to have a constructor that can take in an unsigned int like 0x00FF00FF and interpret it as fully opaque green. I have code for that (I think it should work, could someone check it?):
C++ Syntax (Toggle Plain Text) 
  1. rzb::color::color(unsigned int hex)
  2. {
  3. 	m_red = (hex & 0xff000000)/(0x00ffffff);
  4. 	m_green = (hex & 0x00ff0000)/(0x0000ffff);
  5. 	m_blue = (hex & 0x0000ff00)/(0x000000ff);
  6. 	m_alpha = (hex & 0x000000ff);
  7. }

The thing is, I'd like the user to also be able to give this input: 0x00FF00, and have that also be interpreted as opaque green (alpha value would be FF by default), but I can't figure out how to do that. Is there a way to check the length of a number passed as input (or some other algorithm to do what I want). I can't just compare the values, because 0xffffff (opaque white) comes out to 16,777,215, but 0x0000ffee (slightly transparent green) comes out to 65,518, a smaller value, even though it's the the larger form.
I'm a student. If my statements seem too absolute, feel free to coat them with "In my opinion..." or "I believe...".
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2008
Posts: 401
Reputation: CoolGamer48 is on a distinguished road 
Solved Threads: 40
CoolGamer48's Avatar
CoolGamer48 CoolGamer48 is offline Offline
Posting Pro in Training

Re: check the length of a hex number?

 
0
  #2
Aug 17th, 2008
Wow, nvm - just figured it out.

Have alpha be first, not last.

But if someone could confirm that and/or check the above code I'd appreciate it.
Last edited by CoolGamer48; Aug 17th, 2008 at 11:10 pm.
I'm a student. If my statements seem too absolute, feel free to coat them with "In my opinion..." or "I believe...".
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2008
Posts: 3,828
Reputation: VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute 
Solved Threads: 501
Featured Poster
VernonDozier VernonDozier is offline Offline
Senior Poster

Re: check the length of a hex number?

 
0
  #3
Aug 18th, 2008
•
•
•
•
Originally Posted by CoolGamer48 View Post
Wow, nvm - just figured it out.

Have alpha be first, not last.

But if someone could confirm that and/or check the above code I'd appreciate it.
I don't think you want to be dividing by 0xff, 0xffff, and 0xffffff, but rather by 0x100, 0x10000, and 0x1000000. In particular, 0xff00 / 0xff = 0x100 = 256, which is not in the range of 0 to 255. You can also speed things and use the shift right (>>) operator rather than divide:

C++ Syntax (Toggle Plain Text) 
  1. unsigned int red = (hex & 0x00ff0000) >> 16;
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2008
Posts: 401
Reputation: CoolGamer48 is on a distinguished road 
Solved Threads: 40
CoolGamer48's Avatar
CoolGamer48 CoolGamer48 is offline Offline
Posting Pro in Training

Re: check the length of a hex number?

 
1
  #4
Aug 18th, 2008
Oh, you're right.

But actually, I dropped the system of using different members for red, green, blue, and alpha. I'm just using a single hex value as a member to save space.

Edit:
Just wondering, would this be any faster:
C++ Syntax (Toggle Plain Text) 
  1. unsigned int red = (hex << 8) >> 16;
  2. //or is it:
  3. unsigned int red = (hex << 8) >> 24;
Last edited by CoolGamer48; Aug 18th, 2008 at 1:21 am.
I'm a student. If my statements seem too absolute, feel free to coat them with "In my opinion..." or "I believe...".
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2008
Posts: 3,828
Reputation: VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute VernonDozier has a reputation beyond repute 
Solved Threads: 501
Featured Poster
VernonDozier VernonDozier is offline Offline
Senior Poster

Re: check the length of a hex number?

 
0
  #5
Aug 18th, 2008
•
•
•
•
Originally Posted by CoolGamer48 View Post
Oh, you're right.

But actually, I dropped the system of using different members for red, green, blue, and alpha. I'm just using a single hex value as a member to save space.

Edit:
Just wondering, would this be any faster:
C++ Syntax (Toggle Plain Text) 
  1. unsigned int red = (hex << 8) >> 16;
  2. //or is it:
  3. unsigned int red = (hex << 8) >> 24;
It would be the second one:
C++ Syntax (Toggle Plain Text) 
  1. unsigned int red = (hex << 8) >> 24;

Which one is faster is a great question, one that I don't know the answer to but that hopefully others will.
Reply With Quote Quick reply to this message  
•
•
Join Date: Jul 2008
Posts: 2,001
Reputation: ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of ArkM has much to be proud of 
Solved Threads: 343
ArkM's Avatar
ArkM ArkM is offline Offline
Postaholic

Re: check the length of a hex number?

 
0
  #6
Aug 18th, 2008
Think about 64-bit portability (why not?): hex << 8) >> 24 does not work if sizeof(unsigned int) > 4.
Make user input argument safety in 100% portable manner, for example:
C++ Syntax (Toggle Plain Text) 
  1. rzb::color::color(unsigned int hex)
  2. {
  3.        m_alpha = (hex & 0xFF);
  4.        m_blue   = ((hex>>=8) & 0xFF);
  5.        m_green = ((hex>>=8) & 0xFF);
  6.        m_red     = ((hex >>8) & 0xFF);
  7. }
Reply With Quote Quick reply to this message  
•
•
Join Date: Jan 2008
Posts: 401
Reputation: CoolGamer48 is on a distinguished road 
Solved Threads: 40
CoolGamer48's Avatar
CoolGamer48 CoolGamer48 is offline Offline
Posting Pro in Training

Re: check the length of a hex number?

 
0
  #7
Aug 18th, 2008
Err... ok, ran into a prob again (like my first one). fyi ive gone back to the multiple member system (r,g,b,a as four separate variables). I still can't figure out how to let users pick whether or not to give the alpha bits. If they give (in a ARGB format) 0xee00ff00 (slightly transparent green), I'll read it fine, but if they give 0x00ff00, I'll read the alpha value as 0x00, when it should be 0xff. So my fix didn't really fix anything I guess. Any ideas on how to get this to work?
I'm a student. If my statements seem too absolute, feel free to coat them with "In my opinion..." or "I believe...".
Reply With Quote Quick reply to this message  
Reply

Quick Reply to Thread
This thread is more than three months old.
Perhaps start a new thread instead?
•
•
•
•
•
•
•
•
Message:
•
•
•
•



Similar Threads
Other Threads in the C++ Forum
Thread Tools Search this Thread



api array arrays based beginner binary bitmap c++ c/c++ calculator char char* class classes code coding compile compiler console conversion convert count data database delete deploy developer dll download dynamiccharacterarray email encryption error file forms fstream function functions game generator getline givemetehcodez graph gui homeworkhelp homeworkhelper iamthwee ifstream input int java lib list loop looping loops map math matrix memory multiple news node number numbertoword output parameter pointer problem program programming project proxy python random read recursion recursive reference rpg sorting string strings temperature template text text-file tree url variable vector video visual visualstudio win32 windows winsock word wordfrequency wxwidgets
About Us | Contact Us | Advertise | DaniWeb | Acceptable Use Policy | RSS Feed

©2003 - 2009 DaniWeb® LLC