问题
I've noticed that plenty of opensource project doesn't use BITWISE flags anymore, even if it's fully supported by programming enviroment common for web ( php/Mysql). It's that a "lost practise" for some effective problem, or is just that a lot of php programmers don't know how to handle this type of implementation?
Nothing too important, just very curious :) thanks to you all
回答1:
I'll stick my neck out and say that every technical position requires a sound understanding of bitwise operations.
And I have an anecdote that indirectly addresses the topic.
January 2007 I was in Cochin, India, recruiting for permanent development staff. Since I wasn't involved in the preliminary screening of candidates I had no idea what standard to expect so I had prepared a range of questions and topics ranging from simple understanding of binary and hexidecimal through to architecture, design, and project management.
When I discussed my approach with the Indian HR guy I was (gently) chided for pitching too low. He made it clear that my questions about hex would possibly be construed as an insult to the candidates experience or education.
But my experience of interviewing hundreds of candidates in the UK had fixed in me a conviction that it wasn't possible to pitch too low. My opinion was and still is that if it becomes obvious a candidate is well qualified then it's simple and easy to adjust the level of discussion. I've never had anyone express feelings of being insulted, on the contrary I think a well qualified candidate might feel relieved at a flying start to the interview. It also helps to break the ice and build a rapport needed for a meaningful interview. On the other hand, unqualified candidates usually fall at these lower hurdles.
But not wanting to completely ignore local advice I cautiously decided to include my basic interview topics, and was quite prepared to abandon them if they didn't work.
As the interviews progressed I was glad that I started at that level. It didn't offend anyone, and unsuitable candidates were easily identified.
This is not to say that I expect candidates to deal with bit-twiddling day to day, but whatever the language a sound understanding of the fundamentals of programming is essential. Even developers at the higher levels of abstraction are exposed to hex on a regular basis (RGB values, for example). Parroting stuff you find on the net will only help to the extent that things work perfectly first time.
But for developers starting out in the past five years I believe it's all too easy to gloss over the fundamentals, cosseted by well intentioned IDEs and the meme of "codeless" programming. The Visual Studio installation spash screens boast about developing without writing code. Indeed, does Visual Studio rot the mind?
回答2:
A lot of programmers these days seem to just have their heads filled with just enough knowledge to brute-force code out and then sent into the workforce without being taught what words like "bitwise" even mean.
It's a dying art I tell you...
回答3:
Bitwise operations aren't just about conserving memory. They're really useful for writing clear code. Which would you rather see?
OpenFile("...", true, false)
or
OpenFile("...", writeonly | append)
That's kind of a nonsensical/trivial example, but you get the idea.
回答4:
If you have an already complex application, why would you make it more complex by using bitwise flags. I personally wouldn't use this kind flags if there weren't any more upsides then just being cool. And out of experience, writing it is quite easy, adjusting it later is more harder, let alone if you haven't written it yourself.
Oh and for the record, I do know how to use them.
回答5:
Outside of embedded programming where memory management is critical, their cost outweighs their minimal value. In particular, querying db columns containing bitwise flags produces cryptic SQL that requires referencing the app's code just to determine what value each bitwise operation references.
WHERE (ISNULL(flags, 0) & 4096 = 0 -- What does this bit refer to?
If having to query your DB this way doesn't scare you, it should.
回答6:
Bitfields are very useful if you have very tight memory and speed requirements, or when doing low-level hardware programming.
Unless you are doing embedded programming or something similar, you do not need them. There are far more readable, powerful, extensible mechanisms for performing the same task. For instance, Java's EnumSets.
I would expect a good programmer to know them and not use them :-p
回答7:
"Plenty" is quite generic, we want names! ;-)
Seriously, I come from assembly language and C, and I am quite proficient with bitwise operations. But I wouldn't use them to replace, say 10 unrelated booleans in a class with binary flags in an integer... Unless, perhaps, I have millions of instances of this class!
Should I have to manipulate lot of instance of booleans, I would use some bitset class, to optimize and abstract away these arrays of bits.
Now, bit manipulation fu is almost mandatory in programming, if you want to access to components of RGB[A] values, if you want to call some APIs (even if that's just ORing a number of named flags), etc.
In short, I won't use that in every project I do, but you can't ignore how to do it (a bit like regexes...).
回答8:
I still use bitwise operators, though as my main language of choice (and professionally) is C# I often use Flag enums for it :) But yeah, I think alot of people who code in things like PHP are self taught, and don't know about bitwise operations or the usages of them.
Being self taught myself, I didn't know much about them until I started writing C and C++ code. Now I use them where they make sense :)
回答9:
They always have a place for storing lots of boolean flags in a small amount of space;
Just think if you have 32 flags (for example); You could store them all in one "long integer" and just use up 4 bytes, Now imagine you chose to use a long for each flag (just because the code is easier to maintain - you've now got 128 bytes to deal with.
My background is primarily C/C++ so I was brought up on them so I definately use them in every language I use; but I do agree; newbie programmers tend not to even care - all this memory lying around - who cares?
来源：https://stackoverflow.com/questions/224799/bitwise-flags-abandoned