Description of common errors:
The last line of the error message of Apple Mach-O Linker Error is usually as follows:
Command /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/clang failed with exit code 1
The reason for this error is usually a link error caused by a class of the same name in the project.
It may be that you have two classes with the same name, or it may be because you have defined the same const variable in different .m files.
For this kind of error, you need to look at the long list of paths given in the error message, and find out your duplicate class or variable name to locate the error location.