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duplicate symbols for architectures in Xcode

由 懵懂的女人 提交于 2019-11-28 22:24:24

In your build phases, check to see that you aren't compiling the same file more than once. i.e. If you search for main.m it should only return one result.

If that's not the problem, can you add the code from your main.m to the question?

Voloda2

Check your import files, it may that you're importing a .m file. 

#import "TimeModel.m"

Although the following is not the cause in the OP's case, it was mine, so I'll share it here for anyone facing the same error:

If you are getting a linker error on all global variables, you might need to add extern to their declarations in your header files.

Whether the lack of extern will generate this issue is dependent on build settings, more specifically on "No Common Blocks" under "Apple LLVM - Code Generation" (GCC_NO_COMMON_BLOCKS, -fno-common). If set to yes, which is the default in newer versions of Xcode, you'll get a linker error without extern.

Why extern?

The extern keywords makes it a declaration only (i.e. not also a definition), which since it's a header file is what you want. Some compilers allow it without extern and still 'do the right thing', but omitting extern is discouraged. Which is why newer versions of Xcode by default enable the warning.

Here is a situation in Xcode 7.0 with duplicate symbols error, in case anyone else comes across this scenario

.h file

NSUserDefaults *defaults; // <----placing this above the @interface caused the issue

@interface someViewController

//...

Change to 

.h file

@interface someViewController

{
   NSUserDefaults *defaults;
}

//...

This could happen also when you have the same @interface in different files with different implementations. For example you have a Player class, in the Player.h/m files and you have a Match class (Match.h/m), and a match is between two player, but not the aforementioned Player.

Player.h

@interface Player : NSObject
@property (nonatomic) NSUInteger _id;
@property (nonatomic, strong) NSString* firstName;
@property (nonatomic, strong) NSString* lastName;
@property (nonatomic, strong) NSString* username;
@end

Match.h

@class Player

@interface Match : NSObject
@property (nonatomic, strong) Player* player1;
@property (nonatomic, strong) Player* player2;
@property (nonatomic) NSUInteger matchId;
@end

@interface Player : NSObject
@property (nonatomic, strong) NSString* nickName;
@property (nonatomic, strong) NSString* point;
@property (nonatomic, strong) NSNumber* lastMove;
@end

In this case the the compiler see two different Player class implementation. You need to refactor the Player class in the Match.h file to MatchPlayer.

I ran into an issue where typedef was not added to an enum and the duplicate symbol error appeared between 2 files.

enum <name> {
 ...
} <name>;

By adding typedef before enum fixed the duplicate symbol.

In my case the problem was that .m file was included twice.

PROBLEM:

REASON:

SOLUTION: Leave only one file reference.

If this helps others, that was my case :

I wanted to declare 2 small classes in 1 header and implementation file.

Class 2 is using Class 1

When I got the error this was the situation:
header file - interface+implementation of class 1 , interface of class 2
Implementation file - implementation of class 2

After I moved the implementation of class 1 from header file to implementation file, there was no error and problem solved :
header file - interface of class 1 , interface of class 2
Implementation file - implementation of class 1, implementation of class 2

In my case, I had identical entity name and NSManagedObject names and failed to set the entity Class Codegen to "Manual/None" in the Data Model Inspector.

标签
objective-c
xcode
duplicates
symbols
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