Xcode, Duplicate symbol _main

Question

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.

This can happen if there are multiple occurrences of main() function. — ilgaar, Dec 23 '17 at 20:11

score 92 · Accepted Answer · edited Aug 25 '16 at 08:05

92

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.

edited Aug 25 '16 at 08:05

cjmling

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answered Aug 01 '10 at 06:27

huggie

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I still dont have mine figured out... any other ideas anyone? – logixologist Oct 07 '11 at 03:15
1

you really saved my lots of efforts – Sunil Pandey Jan 25 '12 at 11:13
I had a duplicate main from TBXML (which I just added) – Jacksonkr Jan 26 '12 at 18:19
Thanks! If only I could give you more points... I'm starting to get enough of this XCode bullshit! – Exegesis Jun 05 '12 at 20:00
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This can also happen if you accidentally #import "someFile.m" instead of #import "someFile.h" – Aaron Brager Sep 11 '12 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. – Anupdas Mar 24 '13 at 10:57
Wow! Lots of effort saved! – Dunes Buggy May 01 '15 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. – sarabdeep singh Oct 13 '15 at 20:32
I needed to remove main.m because I was rewriting my AppDelegate in Swift – CodeMonkey Jun 10 '20 at 09:29

score 23 · Answer 2 · answered Oct 10 '12 at 13:19

23

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"

answered Oct 10 '12 at 13:19

dvkch

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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. – Andrei Herford Oct 23 '12 at 11:27
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I had the same problem after changing around the inheritance hierarchy. Thanks. – orkoden Jun 26 '13 at 17:21
Just got bit by this. Thanks! – jsd Nov 21 '13 at 22:55
In my case, I had multiple file "main.m" in my project. This answer helped me! --> http://stackoverflow.com/a/12989012/1881895 – barrast May 27 '14 at 14:13

Stefan · Answer 3 · 2012-08-27T12:39:39.553

16

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

edited Aug 27 '12 at 12:39

answered Aug 27 '12 at 12:24

Stefan

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i made a search by int main and i had two equal files, I removed one and project run. thank you ;) – Pedro Romão Dec 03 '14 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. – John Erck Jan 14 '15 at 17:40

score 8 · Answer 4 · answered Nov 21 '14 at 14:24

8

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.

answered Nov 21 '14 at 14:24

Arbaz Shaikh

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score 3 · Answer 5 · answered Aug 16 '11 at 13:42

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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.

answered Aug 16 '11 at 13:42

Kas1a

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score 3 · Answer 6 · answered Dec 01 '11 at 13:33

3

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

answered Dec 01 '11 at 13:33

Altynbek Usenbekov

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score 2 · Answer 7 · answered Jun 27 '12 at 07:50

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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 ;)

answered Jun 27 '12 at 07:50

InvulgoSoft

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Where should that be? – Kaptain Apr 22 '15 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! – Rémi Santos Oct 20 '15 at 07:36

score 2 · Answer 8 · answered Aug 04 '14 at 23:14

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.

score 1 · Answer 9 · answered Oct 28 '14 at 05:22

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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.

answered Oct 28 '14 at 05:22

Fluffhead

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score 0 · Answer 10 · answered Oct 09 '14 at 00:21

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.

Xcode, Duplicate symbol _main

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