Xcode, Duplicate symbol _main

I have duplicate symbol _main.

The problem is it says "Dupl开发者_如何学Goicate 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.

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.

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"

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

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.

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.

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

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 ;)

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.

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.

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.