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.)


25 Answers 25


How do you sketch Web Interfaces fast?

  • 6
    which one of these has the best answer? – jakc Jan 6 '11 at 11:02
  • 8
    merge and have n users [where n=(number of questions)+(number of answers)] complain on meta about abusive behavior. – abel Jan 11 '11 at 13:03
  • 1
    Not merely duplicates, but off topic. – Raedwald Dec 9 '14 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

  • 79
  • 17
    Apparently he/she has an assignment with a deadline :) – Ken D Jan 12 '11 at 21:17
  • 2
    Four years later, this answer is still a H O O T – Howard Pautz Sep 12 '14 at 5:53
  • 4
    @HowardPautz Six years later, it's still funny. – cat May 16 '16 at 13:53
  • 4
    Don't forget "tanks in advantage" – JAL Dec 3 '16 at 14:22

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 May 17 '10 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. – Chris Marisic Jan 11 '11 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 ;) – Zhaph - Ben Duguid Apr 5 '12 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. – Michael Hampton Oct 4 '12 at 23:36
  • That looks more like a topic than a question archetype. – Simon Kuang May 31 '14 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", 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 to fix 'android.os.NetworkOnMainThreadException'?
**  636**    What is the difference between client-side and server-side programming?
**  628**    How to test multiple variables against a 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?"

  • 18
    The worst part is this question has like 8500 answers all of which work in some ways and don't work in others. – Chris Marisic Jan 11 '11 at 19:04

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?


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

This must come up once a week.

  • 3
    If not more .... – Tim Post Jul 20 '10 at 10:44

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 Aug 3 '09 at 20:36
  • 2
    nobody asking for an indecent profiler? – Thorbjørn Ravn Andersen Jun 4 '11 at 11:23


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 Jul 26 '09 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.


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 Jul 27 '09 at 8:38

In the past:

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


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


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.

  • Haven't got bored yet? :P – Trufa Jan 30 '11 at 21:51
  • @trufa haha, totally forgot about it. Now you've reminded me ;) – jcolebrand Jan 31 '11 at 13:52
  • @drachenstern hehe no worries but don't dare look at me, I'm the laziest bastard you will ever encounter :) – Trufa Jan 31 '11 at 14:58
  • @trufa ~ My motto is that all programmers should be lazy. But not too lazy. (mainly in re: functions and reuse, etc. Copy-paste twice, but after that make a function and quit copy-pasting, too much effort to do so, making a function makes you lazier ... blah blah TL;DR ;] ) – jcolebrand Jan 31 '11 at 15:30
  • @drachenstern codinghorror.com/blog/2005/08/… – Trufa Jan 31 '11 at 15:55
  • @trufa ~ SEEEEEE!!!! ;) :D – jcolebrand Jan 31 '11 at 16:17

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


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..

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