Xcode 10 Error: linker command failed with exit code 1

go to your project directory in the terminal

Type:

pod deintegrate
pod install

In your project, open the Project Navigator, and expand the Frameworks folder. You will see the file -lstdc++.6 highlighted in red, delete it, rebuild your project and you're good to go.

Open the projectname.xcworkspace if you are using cocoapods not the projectname.xcodeproj.

Alternatively, using terminal

$ open projectname.xcworkspace

Hope this helps.

I had this problem today in C++ using a newly upgraded Xcode 10 in a project that does not use pods, unlike the other answers.

When I clicked on the linker error there were no details given. This stumped me for a while and then I realised you can right-click the linker error and click "reveal in log".

In my case it was just a function that I had renamed-but-not-updated-all-the-references-to-it causing a linker error, but the real problem was that the linker error details were not being shown when the error occurred.