Xcode build failure "Undefined symbols for architecture x86_64"

For me, this started to happen after merge conflict.

I tried to clean and remove build folder, but none of it helped. This issue kept happening regardless. Then I relinked the reference by deleting the groups that was problematic and re-added to the project and it worked.

Could also be an `#include <windows.h>` in the .c file that you're trying to compile.

I also encountered the same problem , the above methods will not work . I accidentally deleted the files in the following directory on it .
[![enter image description here][1]][1]


Or

~/Library/Developer/Xcode/DerivedData/

[![enter image description here][2]][2]


[1]:

[2]:

Under Xcode 9.0b5 you may encounter this because Xcode 9.0b5 has a bug in it where when you add source code, it does not honor the target settings. You must go in and set each file's target manually afterwords:

[![Xcode project with manual target membership illustration][1]][1]


[1]:

In my case, I built a custom framework with Deployment target set to 9.1, but the Deployment target of my app was lower, which supports 8.1. Minimize the custom framework Deployment target solved my problem.

I know it's an old question but today got the same error and non of the above solutions worked.

Have fixed it however by setting option:

Project -> Architecture -> Build Active Architecture Only

to Yes

and project compiles and builds properly

I am late to the party but thought of sharing one more scenario where this could happen.
I was working on a framework and was distributing it over cocoapods.
The framework had both objective c and swift classes and protocols and it was building successfully.
While using pod in another framework or project it was giving this error as I forgot to include .m files in podspec.
Please include .swtift,.h and .m files in your podspec sources as below:
s.source_files = "Projectname/Projectname/**/*.{swift,h,m}"

I hope it saves someone else's time.

in my case I had to add
```
target 'SomeTargetTests' do
inherit! :search_paths
end
```
to my podfile and then delete the /Pods directory and run `pod install`

(Xcode 10.1)

This might help somebody. It took me days to finally figure it out. I am working in OBJ-C and I went to:

`Project` -> `Build Phases` -> `Compile sources` and added the new `VC.m` file I had just added.

I am working with legacy code and I am usually a swifty, new to OBJ-C so I didn't even think to import my `.m ` files into a sources library.

EDIT:

Ran into this problem a second time and it was something else. This answer saved me after 5 hours of debugging. Tried all of the options on this thread and more. <https://stackoverflow.com/a/13625967/7842175> Please give him credit if this helps you, but basically you might need to set your file to its target in file inspector.

[![This is your file inspector, just make sure all the targets you need are "ticked"][1]][1]


[1]:

All in all, this is a very vague Error code that could be caused for a lot of reasons, so keep on trying different options.

Sometime, I forget to copy library from Release-universal and mistakenly copy from Release-iphoneos. Usually Release-iphoneos contains .a file which has been pruned for X86. and so it gives the error.