Linker can´t find symbols

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Created Apr ’22

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Hello folks, I am new to MacOS/iOS and ran into the following problem (IDE is Xcode13): I have made a small c++ audio library with the Juce framework that I want to integrate into an existing application running on MacOS and iOS.

So far so good, I added the Projucer library project as a subproject to my workspace, added the correct header paths, added the subproject as a dependency and linked the library in the build settings of the target, so I can directly test changes I make to the library in the app (for now it is only a small c++ console app for testing since I wanted to find out how to correctly import the library before writing the bridge, as described here: https://github.com/adamski/audioengine-demo).

The problem I am currently running into is the following linker error I cant resolve:

Undefined symbols for architecture arm64:

ld: symbol(s) not found for architecture arm64

This error occurs 101 times, for every juce function that is beeing used. I checked the target architecture settings in both the library and the console app, they are the same. If I change the build active architecture only setting to No, the error changes to

ld: symbol(s) not found for architecture x86_64

I analysed the library binary with the file command in the console, which led to following output:

mylib.a : Mach-O universal binary with 2 architectures: [arm64:current ar archivecurrent ar archive] [x86_64]

mylib.a (for architecture arm64): current ar archive

mylib.a (for architecture x86_64): current ar archive

In my understanding, the binary should support my architecture (arm64), so why cant the linker find the symbols?

Thanks for your help!

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Answer 1

DTS Engineer OP

Apple

Apr ’22

I suspect that the architecture stuff is a red herring. If you had an architecture mismatch, you’d get a different error (the linker would be complaining that it couldn’t find the architecture in your library file).

The most common cause of problems like this is C++ name mangling. Folks implement a library in C++ without added extern "C" { … } and then try to call it from C (or Objective-C). C++ uses a mangled symbol and C uses a nonmangled one, and you get a link error.

However, I’m not sure that’s the case here because you’re trying to use the library from a C++ client, and so both sides should mangle the same way.

What sort of library is it? Static (.a)? Or dynamic (typically .dylib)? If you’re not sure, run the file command-line tool against the library and see what it prints.

Oh, one last thing: You tagged your question with both iOS and macOS. Be aware that these are different platforms, and the platform matters when it comes to building library code. For example:

Intel code built for the iOS simulator is not the same as Intel code built for the Mac.
Arm code built for iOS is not the same as Arm code for an Apple silicon Mac.

Make sure you’re not mixing your platforms.

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