ld: Undefined symbols for architecture armv7

ld link 的时候错误，xcode报出的错误完全可以找出原因所在。如：

1、lib缺少

2、lib冲突（这个再用protobuffer的时候碰到过，一开始添加的工程，后来编译成lib添加的，导致了lib冲突；而且xcode报的错也能够看的出来，在生成的product里面有了一个libproto，把DerivedData都删除了之后，就没问题了，"/Users/user/Library/Developer/Xcode/DerivedData/TZoomClass-ctuyrarprdihvhdtltssdsfhvfuz/Build/Products/Debug-iphoneos/"）

3、lib本来就不支持armv7

http://stackoverflow.com/questions/6429494/undefined-symbols-for-architecture-armv7

Common Causes

The common causes for "Undefined symbols for architecture armv7" are:

1. You import a header and do not link against the correct library. This is common, especially for headers for libraries like QuartzCore since it is not included in projects by default. To resolve:
   • Add the correct libraries in the Link Binary With Libraries section of the Build Phases.
   • If you want to add a library outside of the default search path you can include the path in theLibrary Search Paths value in the Build Settings and add
     -l{library_name_without_lib_and_suffix} (eg. for libz.a use -lz) to the Other Linker Flags section of Build Settings.
     
2. You copy files into your project but forgot to check the target to add the files to. To resolve:
   • Open the Build Phases for the correct target, expand Compile Sources and add the missing .m files. If this is your issue please upvote Cortex's answer below as well.
     
3. You include a static library that is built for another architecture like i386, the simulator on your host machine. To resolve:
   • If you have multiple library files from your libraries vendor to include in the project you need to include the one for the simulator (i386) and the one for the device (armv7 for example).
   • Optionally, you could create a fat static library that contains both architectures.