Xcode, Duplicate symbol _main

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I have duplicate symbol _main.

The problem is it says "Duplicate symbol _main in /Users/.../i386/main-B9843B6026D6EFA4.o and /Users/.../i386/main-B9843B6026D6EFA4.o", the XXX and XXX are actually the same .o file. I don't know why it thinks it's duplicate symbol when it's the same .o?!

Any help appreciated, thanks.

Loireatlantique answered 1/8, 2010 at 6:13 Comment(1)

This can happen if there are multiple occurrences of main() function. – Dotti 23/12, 2017 at 20:11

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Ah..I figure out it's that I have multiple entries under Targets/Compiled Sources ( in newer XCode it's under Build Phases/Compile Sources ). I removed them and the problem is solved. The multiple entry thing probably has to do with Git merge.

Loireatlantique answered 1/8, 2010 at 6:27 Comment(9)

I still dont have mine figured out... any other ideas anyone? – Tanning 7/10, 2011 at 3:15

you really saved my lots of efforts – Addam 25/1, 2012 at 11:13

I had a duplicate main from TBXML (which I just added) – Alainealair 26/1, 2012 at 18:19

Thanks! If only I could give you more points... I'm starting to get enough of this XCode bullshit! – Lobel 5/6, 2012 at 20:0

This can also happen if you accidentally #import "someFile.m" instead of #import "someFile.h" – Barberabarberry 11/9, 2012 at 15:35

I have had a similar error when i recreated a subclass of NSManagedObject and gave the option to replace instead of just removing the file and recreating. Thanks for the tip. – Cognomen 24/3, 2013 at 10:57

Wow! Lots of effort saved! – Exurbia 1/5, 2015 at 18:39

it happened to me when i tried to import some other project code in my project. Xcode added main.m file from imported source code to compile sources for my parent project target. Thanks lot @huggie. you saved lot of time for me. – Riviera 13/10, 2015 at 20:32

I needed to remove main.m because I was rewriting my AppDelegate in Swift – Acetal 10/6, 2020 at 9:29

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It appeared that in my case I was importing a .m file instead of its .h counterpart. Solved by editing

#import "Tools.m"

into

#import "Tools.h"

Patriarchy answered 10/10, 2012 at 13:19 Comment(3)

Thank you so much! After I tried all other solutions a simple search for .m" in my project showed the import of an .m file. – Zetta 23/10, 2012 at 11:27

I had the same problem after changing around the inheritance hierarchy. Thanks. – Ambassadress 26/6, 2013 at 17:21

In my case, I had multiple file "main.m" in my project. This answer helped me! --> https://mcmap.net/q/103399/-duplicate-symbols-for-architectures-in-xcode – Windbag 27/5, 2014 at 14:13

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I also had this problem and it was caused by code I imported from another project. I did a grep for "int main" in my project directory:

grep -nr "int main" .

and found

./main.m:13:int main(int argc, char *argv[])
./IMPORTED_DIR/main.m:13:int main(int argc, char *argv[])

the IMPORTED_DIR contained the extra main.m that was causing the error for me

I removed that file from the Project -> Targets -> Build phases -> Compile sources list and then it compiled

Pahoehoe answered 27/8, 2012 at 12:24 Comment(2)

i made a search by int main and i had two equal files, I removed one and project run. thank you ;) – Wing 3/12, 2014 at 16:53

I ran grep -nr "int main" . and found a sample project within my project that came in as part of an SDK download that I added. After finding this out, I deleted those files via Xcode and voilà! The project now builds. Thanks. – Jackscrew 14/1, 2015 at 17:40

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I was facing the same issue with using two third party framework. (AppLovin and Flurry) And I came to know that by removing "all_load" from "Other Linker Flags" in build settings.

Arther answered 1/8, 2010 at 6:14 Comment(0)

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I had the same problem opening a project, that was created with Xcode 4.0.2, with Xcode 4.1. I simply solved by clicking on "Modernize Project" (Editor/Modernize Project). This procedure automatically removed all duplicates.

Supplemental answered 16/8, 2011 at 13:42 Comment(0)

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If still have a problem, try to search like this: "int main(", and remove those files except main.m

Verger answered 1/12, 2011 at 13:33 Comment(0)

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Just got this problem myself, but after reading huggie's solution which did lead me on the right track, I was left a bit confused. So current solution in Xcode: Choose project, target -> build phases and click validate settings

Then Xcode will auto fix its own mistake. It is always nice when the tools tries to stop your progress ;)

Meg answered 27/6, 2012 at 7:50 Comment(2)

Where should that be? – Horrid 22/4, 2015 at 13:43

This is awesome, never seen this before. Just go to your project build phases, and you can find Validate Settings in Editor menu. Worked for me! – Luscious 20/10, 2015 at 7:36

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In my case, I declared an NSString in my constants file (imported by many classes) but forgot to define it as static!!

e.g. NSString* PARAMS = @"paramA"; should be: static NSString* PARAMS = @"paramA";

Reading the full error message allowed me to figure this out: "Duplicate symbol PARAMS". Don't be afraid and try to understand error messages! Sometimes they might even tell you exactly what you did wrong.

Montcalm answered 4/8, 2014 at 23:14 Comment(0)

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In my case, I had imported another project, in order to utilize a library contained within. It resulted my project having two main.m files.

This was even more confusing, since the error didn't show up until several builds later.

Hersch answered 28/10, 2014 at 5:22 Comment(0)

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You can get this for method names too!

I got duplicate symbol _runOnMainQueueWithoutDeadlocking after adding DBCamera via CocoaPods and it was because both my category on NSObject (NSObject+Tools.h) and the GPUImage dependency file GPUImageOutput.m both had a method called 'runOnMainQueueWithoutDeadlocking'.

I was fortunate enough to be able to remove my method from code because I wasn't actually using it anymore or anywhere.

It's probably what I deserve for putting a category on NSObject.

Endurant answered 9/10, 2014 at 0:21 Comment(0)

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