Duplicate Symbol Error in Objective-C build?

Question

I got this error when I press build+debug:

ld: duplicate symbol .objc_class_name_BlogTableItemCell in /Users/fabian/Development/Workspaces/iphone_experiments/xcode_build_output/MausLog.build/Debug-iphonesimulator/MausLog.build/Objects-normal/i386/BlogTableItemCell-3733583914888A7B.o and /Users/fabian/Development/Workspaces/iphone_experiments/xcode_build_output/MausLog.build/Debug-iphonesimulator/MausLog.build/Objects-normal/i386/BlogTableItemCell-3733583914888A7B.o
collect2: ld returned 1 exit status
Command /Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/gcc-4.2 failed with exit code 1

Do not make the @implementation part inside the .h file. – Teddy Feb 22 '15 at 18:38 — Teddy, Feb 22 '15 at 18:38

score 176 · Answer 1 · edited Jul 06 '19 at 04:05

176

You could also get this error if you mistakenly let Xcode's auto-complete for #import statements specify the '.m" file for the 'duplicate' class instead of the '.h'.

edited Jul 06 '19 at 04:05

Cœur

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answered Apr 24 '11 at 20:33

One of the best catches ever! – Michael Gaylord Mar 29 '12 at 20:50
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I wish there was some way to change THIS answer to the accepted answer. – race_carr Mar 14 '14 at 19:56
Excellent. This just happened to me and my heart stopped beating for a moment. – Alex Zavatone Nov 07 '17 at 01:27

score 64 · Accepted Answer · answered Feb 15 '10 at 07:41

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It seems that you are compiling the same BlogTableItemCell class two times in different places of your code. This may happen in the following cases.

You have put the same class implementation into two different files;
You actually have just one implementation of this class, however you are also linking in your project a framework or library containing a class whose name is exactly the same of yours.

Try finding in the whole project your class and make sure only one copy is available within your project.

answered Feb 15 '10 at 07:41

Massimo Cafaro

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1.You have put the same class implementation into two different files; -> I checked that with "Find in Project". There is only one file! 2. "linking in your project a framework or library containing a class whose name is exactly the same of yours." -> I also checked that with "Find in Project". There is only one link at the right position. Any suggest how to go from here? – fabian Feb 15 '10 at 08:32
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Alright i got it. Xcode had an old reference to the file in the class explorer. Thanks – fabian Feb 15 '10 at 08:39
I had this same problem when I integrated the Facebook SDK (which included SBJson files) into a project I was using that already had those same SBJson classes. Having two copies was causing the error. Finally, I deleted one set of those files and then the problem was resolved. – Eric Brotto Nov 04 '11 at 11:28
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Just ran into this error ... I was importing "*.m" instead "*.h" files in one of my implementations! – Christoph Jun 09 '13 at 22:44
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I run into this problem when I make it both in the target and in the test. – huggie Dec 10 '13 at 10:47
Copy-pasting a class...I forgot to change the implementation name :-O – jomafer Sep 23 '14 at 15:18
thanks @ChristophH. ! this is a very common error it seems – Greg Aug 18 '15 at 01:49

score 43 · Answer 3 · edited Nov 21 '15 at 22:43

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For me, changing 'No Common Blocks' from Yes to No ( under Targets->Build Settings->Apple LLVM - Code Generation ) enter image description here

edited Nov 21 '15 at 22:43

Brad Larson

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answered Nov 21 '15 at 16:12

NeilNie

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Brad: you saved me the day !! – stefat Nov 25 '15 at 18:39
Wow that was exactly what happening to me. Thanks – Jeremy Luisetti Sep 14 '16 at 09:25
You're a rock star. – Stateful Oct 01 '16 at 19:32
this must be a solution but in my case I'm using an 3rd party application, it internally using same framework file which I'm using in my project. Any solution you can refer ? – CoDe Jan 21 '17 at 09:02

score 25 · Answer 4 · answered Feb 17 '12 at 02:33

I had a similar problem due to poor defining of consts. I had defined a const in my header:

int const kCropLocationTop = 1;

This was presumably imported multiple times. To fix i changed the header def as follows:

extern int const kCropLocationTop;

and moved the assigning of the const to the .m file:

int const kCropLocationTop = 1;

Hope that helps anyone who's as ignorant of simple objective c concepts as I am!

score 18 · Answer 5 · answered Jul 04 '12 at 07:16

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By mistake the source file was included twice in the Project -> Build Phase -> Compile Sources. Removing one of them solved the problem.

answered Jul 04 '12 at 07:16

Pratik

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Thanks, exactly what I needed. Lots of people here said the issue was things being added twice, but didn't explain how to remove it. – shim Sep 25 '12 at 05:29
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Same problem for me. This happened following a svn merge and resolving conflicts in the project.pbxproj – Thomas Desert Nov 16 '12 at 14:02
THIS. How come this answer has only 9 upvotes? Seems like it's the only cause I ever run into when I get linker errors. I would like to upvote this 10 times. – KPM Apr 14 '15 at 12:30
Bad auto merge from git caused a dup in my project file. Another dev had renamed a bunch of files. To fix it I had to remove both copies and re-add a single copy. – Kibitz503 Nov 03 '15 at 02:47
Thanks !! you saved my day (y) – Bablu Joshi Aug 18 '16 at 06:16

score 18 · Answer 6 · edited May 23 '17 at 10:31

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iPhone: Duplicate Symbol Error? by user576924

answered it correctly for me. However to find the offending gremlin this ZSH snippet.

grep "import.*\.m" **/*.[hm]

Will immediately tell you where your error is.

edited May 23 '17 at 10:31

Community

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answered Nov 03 '11 at 18:56

bradgonesurfing

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Thanks for this. I think it can be summed up as: Don't try to `#import` .m files! – Jason Moore Apr 18 '12 at 10:58
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Could perform a similar search in Xcode. Search the whole project (Command-Shift-F) for `.m"` and `.m>`. Both should be sufficient to find the offending line. – timgcarlson Feb 12 '15 at 23:10

JohnVanDijk · Answer 7 · 2015-07-24T10:29:46.573

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The most common reason for this error is importing an xyz.m file instead of the xyz.h file. Check if your imports contain something like #import "----.m"

edited Jul 24 '15 at 10:29

answered May 30 '13 at 05:33

JohnVanDijk

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score 4 · Answer 8 · answered Aug 22 '12 at 15:27

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Just to add; Using Xcode to generate subclassed managed objects (Core Data) can sometimes duplicate the generated files. For me the fix was to delete the generated files and re-generate them.

answered Aug 22 '12 at 15:27

ChargedNeuron

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score 3 · Answer 9 · answered Jul 07 '11 at 13:17

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I just ran into this problem myself. For the list, here's another possibility:

Duplicated linking line in the project file.

I caused this merging conflicts on a SVN update, when I accidentally duplicated a line.

answered Jul 07 '11 at 13:17

DBD

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score 2 · Answer 10 · answered Oct 22 '13 at 12:29

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It happened to me, too. In my case, one (just one) of my core data automatically generated classes was inserted twice. I spotted the duplication by looking at Build Phases...Compile Sources. Simply deleting one of the occurrences solved the problem.

answered Oct 22 '13 at 12:29

Bruce Cichowlas

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score 2 · Answer 11 · answered Feb 12 '15 at 23:18

Adding another possible cause to the list... you may have mistakingly created multiple constants in the implementation file, but outside of the implementation, with the same name.

In HeaderFileOne.m

NSString * const kCoolConstant = @"cool";

In HeaderFileTwo.m

NSString * const kCoolConstant = @"cool";

So changing one of those constant names would fix the compile error.

score 2 · Answer 12 · answered May 04 '16 at 09:45

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This may help someone

I got this error because I duplicate a ViewController and then renamed it. So when I compile I got this error. The reason was in both of the view controllers there was a "float" variable with same name i.e "float padding=10.0" which I had defined on class level. Renaming the name of the above mentioned variable in One of the view controllers solved my problem.

answered May 04 '16 at 09:45

Muhammad Nayab

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I have the same situation - my question is: why is this a problem? Surely two classes can have the same internal variable name... – Joe Sep 27 '17 at 09:33

score 1 · Answer 13 · answered Aug 12 '15 at 07:56

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I also faced to this problem. My solution was rename one of global variable, which has the same name as one in other class. Hope this helps

answered Aug 12 '15 at 07:56

rgreso

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score 0 · Answer 14 · answered Sep 28 '12 at 17:09

The same thing happened to me while I was playing with localizable xib files, accidentally I have created two implementation files and appereantly that caused the problem in my case. After deleting / recreating the implementation file without doing the same mistake, the error was fixed.

score 0 · Answer 15 · answered Feb 04 '16 at 03:02

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One of our developers left the "libSoomla*" project files in there twice. I removed the duplicate soomla files, re-built, and that fixed it!

Hope it helps.

answered Feb 04 '16 at 03:02

Pim de Witte

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score 0 · Answer 16 · edited May 23 '17 at 12:34

In may case, I followed some instructions to build a newer version of Subversion which directed me to create this symbolic link:

ln -s /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/ /Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.10.xctoolchain

Now I'm really a Windows guy so it wasn't immediately obvious to me - but removing the link fixed it for me (after restarting XCode):

rm /Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.10.xctoolchain

Phew.

(The actual error I got was the one described here: build error duplicate symbols arclite.o)

score 0 · Answer 17 · answered Dec 18 '17 at 06:54

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Make sure that you didn't import .m File . For me this happen I added #import "SchoolCommuterHome.m" instead of #import "SchoolCommuterHome.h"

answered Dec 18 '17 at 06:54

Mehedi Hasan

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Duplicate Symbol Error in Objective-C build?

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