Strongly related: How do we deal with octuplicate questions?

This is not a question about how to deal with duplicates, it's a simple "meta" question:

What is the most rampant duplicate on Stack Overflow?

  • The particular duplicate must be "alive" on Stack Overflow (not merged or closed duplicate)
  • The duplicate-ness must be pretty unquestionable.

For example:

This is a duplicate of score 2 1.

They are both so close that it makes little sense to have separate questions.

However, score 2 is pretty uninteresting.

(The rationale of this question is to find the duplicates so we can get the administrators to merge them. It is also to find better ways to find dupes in the first place, and perhaps turn finding duplicates into a game.)

  • How is the "score" of a duplicate determined? The total number of duplicates? Commented Jul 26, 2009 at 5:51
  • Yerp, total number of "live" duplicates
    – waffles
    Commented Jul 26, 2009 at 5:54
  • 36
    With true irony, is this a duplicate? How do we deal with octuplicate questions? Commented Jul 26, 2009 at 8:55
  • 5
    Marc, this is about the search for the most rampant duplicate, which is one possible solution to the duplicate problem. its not about solving the problem, it a much narrower, and hopefully more fun question.
    – waffles
    Commented Jul 26, 2009 at 11:35
  • One that comes up again and again is floating point comparisons e.g. "why is if (myFloat == 23) not working?"
    – ChrisF Mod
    Commented May 17, 2010 at 11:54
  • 7
    @mmyers is correct, this question is itself a dupe: What's the most repeated question on StackOverflow? Commented May 17, 2010 at 22:19
  • 1
    @Josh: No, this question came months before the other.
    – mmyers
    Commented May 18, 2010 at 1:01
  • @mmyers: Oh, you're right. Sorry! :-) Commented May 18, 2010 at 3:23
  • See this question for another 5 candidates + 2 more in the answers. Commented May 24, 2010 at 15:01
  • 2
    I'm pretty sure "Regular Expression Help" gets asked most often, but we always change its title to something a bit more descriptive. Commented Jan 6, 2011 at 0:45
  • 1
    Fantastic question -- at last a rep-incentive for closing dupes, and look ma no code changes! (Even if it's only meta-rep.) IMHO it should be a requirement to list all the question URLs in your answer to get upvotes here. Commented Jan 26, 2011 at 8:06
  • Ironic that I also posted a duplicate: Are duplicates creating broken windows? Commented Oct 5, 2012 at 0:00
  • Question title that doesn't describe the problem
    – Pollyanna
    Commented Jan 17, 2014 at 19:31
  • stackoverflow.com/questions/linked/203198?lq=1
    – Kevin B
    Commented Jan 24, 2014 at 22:16
  • What is the most rampant duplicate on Stack Overflow. Now do the actual title, please. (cross-site)
    – Mazura
    Commented Feb 9, 2020 at 4:31

25 Answers 25


How do you sketch Web Interfaces fast?

  • 7
    which one of these has the best answer?
    – jakc
    Commented Jan 6, 2011 at 11:02
  • 8
    merge and have n users [where n=(number of questions)+(number of answers)] complain on meta about abusive behavior.
    – abel
    Commented Jan 11, 2011 at 13:03
  • 2
    Not merely duplicates, but off topic.
    – Raedwald
    Commented Dec 9, 2014 at 18:07

How to parse HTML with RegEx?

...by far has the most dupes.

... just to name a few.


I guess it is:

Me no can get program working - you help please code here pls debug. Thxxxx

  • 80
    – Pops
    Commented Jul 15, 2010 at 18:55
  • 20
    Apparently he/she has an assignment with a deadline :)
    – Ken D
    Commented Jan 12, 2011 at 21:17
  • 3
    Four years later, this answer is still a H O O T Commented Sep 12, 2014 at 5:53
  • 5
    @HowardPautz Six years later, it's still funny.
    – cat
    Commented May 16, 2016 at 13:53
  • 4
    Don't forget "tanks in advantage"
    – JAL
    Commented Dec 3, 2016 at 14:22
  • @JAL: Related Commented May 20, 2023 at 14:27

On Server Fault, it's definitely "How do I host my server from home":

(And that's not even all of them.)

Which is ridiculous because the answer is always "Don't" - and I thought this was a site meant for professionals...

  • 2
    Well, sometimes "don't" is the proper and professional answer... but that's a different discussion for a different time. I would have figured that was a prime target for duplicates, I just never expected that much ... variety ... in the wording.
    – AnonJr
    Commented May 17, 2010 at 18:23
  • Don't is definitely not the answer, the answer comes in regards to availability guidelines. If you only LIKE to have your site up, be all means host from home. If you NEED your site up. Use a real host. Commented Jan 11, 2011 at 19:03
  • 1
    What's scary is the same answer applies to "How to parse HTML with RegEx" - again the ideal answer is "Don't" but there are some limited cases where it's possible ;) Commented Apr 5, 2012 at 9:52
  • 1
    As of today, a search for +host +server +home turns up 1,153 results on SF. Not all of them are this question, but it appears that the vast majority are. Commented Oct 4, 2012 at 23:36
  • 1
    That looks more like a topic than a question archetype. Commented May 31, 2014 at 5:51

Since Jarrod spent so much time and effort cleansing the data, I figured it'd be a shame not to have some fun with it.

Here are the top 30 questions (by # of questions closed as duplicates of them) on SO:

9363    What is a NullPointerException, and how do I fix it?
4533    How do I return the response from an asynchronous call?
4070    What is a NullReferenceException, and how do I fix it?
3304    "Notice: Undefined variable", "Notice: Undefined index", "Warning: Undefined array key", and "Notice: Undefined offset" using PHP
2974    How do I compare strings in Java?
2937    PHP parse/syntax errors; and how to solve them
2271    What is an undefined reference/unresolved external symbol error and how do I fix it?
2240    mysql_fetch_array()/mysql_fetch_assoc()/mysql_fetch_row()/mysql_num_rows etc... expects parameter 1 to be resource
1884    Reference - What does this error mean in PHP?
1850    PHP mail function doesn't complete sending of e-mail
1745    Is floating point math broken?
1642    How to fix "Headers already sent" error in PHP
1398    Event binding on dynamically created elements?
1391    JavaScript closure inside loops – simple practical example
1325    How can I prevent SQL injection in PHP?
1259    When to use single quotes, double quotes, and backticks in MySQL
 968    Why are these constructs using pre and post-increment undefined behavior?
 906    Why can templates only be implemented in the header file?
 859    What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?
 855    UTF-8 all the way through
 842    How do you parse and process HTML/XML in PHP?
 810    How to access the correct `this` inside a callback
 794    Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference
 754    Reference - What does this regex mean?
 745    Can I mix MySQL APIs in PHP?
 724    Is Java "pass-by-reference" or "pass-by-value"?
 703    Scanner is skipping nextLine() after using next() or nextFoo()?
 685    How can I fix 'android.os.NetworkOnMainThreadException'?
 636    What is the difference between client-side and server-side programming?
 628    How to test multiple variables for equality against a single value?

(And yes, I'm counting deleted posts too - lookin' at you, PHP)

select top 30 count(*) as dups, 
  concat('site://q/', RelatedPostId, '|', isnull(q.Title, RelatedPostId)) as Q,
 iif(max(q.ClosedDate) is not null, '*', '') as Closed,
 iif(max(q.DeletionDate) is not null, '*', '') as Deleted

from PostLinks
 join PostsWithDeleted q on q.Id=RelatedPostId

where LinkTypeId=3

group by RelatedPostId, q.Title
order by count(*) desc

This is now available for your use and abuse on the Stack Exchange Data Explorer!


The worst offender in my books is "How do I run multiple versions of IE on the same machine?"

Dupes of Running Internet Explorer 6, Internet Explorer 7, and Internet Explorer 8 on the same machine:

It goes on and on and it depresses me to no end.


One I see often is "How do I center an element vertically and horizontally with CSS?"

  • 19
    The worst part is this question has like 8500 answers all of which work in some ways and don't work in others. Commented Jan 11, 2011 at 19:04

Attempting to modify a C string results in an access violation:

This must come up once a week.


Should I learn Emacs?

Will Emacs make me a better programmer?
Is it worth investing time in learning to use Emacs?
Should I learn to use Emacs?
Are there any reasons why a C# developer should learn Emacs/Vim?
Would you recommend vim/emacs for beginner programmers?
Is it worth learning to use Emacs for web development

How to learn Emacs?

How do you learn proper Emacs?
How to quickly get started at using and learning Emacs
Resources for learning Emacs
Forcing myself to master Emacs

Emacs/Vim vs IDEs is popular, though not really exact duplicates per se, they are all editor vs different IDE questions.

What specific productivity gains do Vim/Emacs provide over GUI text editors?
From Visual Studio to Vim or Emacs? (closed subjective, not dupe)
Why Emacs/Vim/Textmate? Isn't Xcode good enough?
Why should I use an IDE?
What are the efficiencies afforded by Emacs or Vim vs Eclipse?
C++ development on linux Code::Blocks, EMACS or GVIM
Which editors out of Emacs, Vim and JEdit support multiple simultaneous text insertion points?
Emacs in the era of IDEs
What modern editors compete with emacs/vi?
Java programming environment : emacs or eclipse?
Eclipse, is there a reason to chose it over emacs or vi?


I have a 3 pointer:

Any decent C# profilers out there? Best .NET memory and performance profiler? What Are Some Good .NET Profilers?

Really they should all be folded into a single mega community wiki .... There is no value in having the 3 questions.

  • Agreed, they should probably be merged. 3 points for you :)
    – Jonik
    Commented Aug 3, 2009 at 20:36


That's a duplicate score too high to count.

  • 1
    Eric, there is no clear unambiguous list for the moderator to work with. See how Marc was able to resolve the dupe I posted in seconds. Surely you could beat my measly score of 2.
    – waffles
    Commented Jul 26, 2009 at 14:30

"foreach captured variable c#"

Jon kindly listed some of them here... and that was just in November; it will be longer now...

The problem with this language gotcha is that until you understand what is happening, you can't know what to look for... IMO, this is one of the good use-cases for tag-specific home pages, where we can (manually) add a FAQ for that tag (i.e. link to the canonical answer).


Data query tested in 2016

Shog9's Data Explorer query didn't seem to work for me, so I crafted one that did: https://data.stackexchange.com/stackoverflow/query/254033/rampant-duplicates-questions-with-the-most-duplicates

  l.RelatedPostId AS [Post Link],
  COUNT(l.PostId) AS DupCount
  PostLinks l
  l.LinkTypeId = 3
  DupCount DESC

This is quite "rampant": Best Java 7 features

Pretty much exact duplicate of What new features in java 7 do you find most useful? (posted 9 months earlier), very close to What are you looking forward to in Java 7? (6 months earlier), and somewhat close to many others.

What also springs to mind are the countless variations on the theme "What is the best Python (web) framework?", with ever so subtle differences in emphasis and formulation. (Right now I'm not delving too deep into those, but take a look at python+frameworks, python+framework and python+web-frameworks.)


Android has some serious flaws in its touch event model, and this has caused many people to ask how to fix the problem (the real answer seems to be "upgrade to Gingerbread", sadly):

I've marked most of these of dupes of the original, not sure if merging or what is the solution here. The bug report mentioned in 4342464 is the most correct answer IME.


In the past:

[Why/When] Should I use xxxx Programming Language?


Concatenate row values into a single column is fairly common for SQL Server


  • Can you create a list of actual merge candidates, so I can score it :p
    – waffles
    Commented Jul 27, 2009 at 8:38

I feel like mod_rewrite should be on this list but I'm too lazy to go look up a lot of duplicates. I'll mark it CW and someone who's motivated (or tomorrow when I'm bored I) can go look some up.


Anything where the answer is dos2unix. The symptoms are varied and the clue quotient of the OPs is mostly, shall we say, chequered. In the end, by the time it's solved, it's obviously off-topic for SO, but you see some good programming and debugging coaching in the speculations leading up to that.

The examples I am finding are less spectacular than the best I've seen. These all contain literally dos2unix in the answer, but there will be hundreds more with different wording.


Having voted to close more than 1600 questions, and succeeding in many of them, these are the two I found (anecdotal) most annoying (in number, yes) from C#/.NET world:

  1. Get property name and type using lambda expression

  2. And even more duplicated is this: Conditional operator assignment with Nullable<value> types?

  3. And even more: Pass An Instantiated System.Type as a Type Parameter for a Generic Class

That's just from my experience. The language designers can take a cue to find the most requested feature..


I'm interested in Java, but every Java regular expression question I see seems to be "plz send me teh regex".


I'm pretty sure the one I encounter the most is along the lines of "How come .1 + .1 + .1 doesn't equal .3?".

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