1、Undefined symbols for architecture：
(1) extern variable所致，在.h文件中声明exter T variable,在.m文件中定义T variable = value即可。
(2) sqlite所致，there are two ways can resolve it:
(i) add libsqlite.dylib to "Link Binary With Libraries".
(ii) set a value called "-lsqlite3" to "Other Linker Flag".
2、the bundle could not be loaded because it is damaged or missing necessary resources：http://stackoverflow.com/questions/25079775/test-bundle-could-not-be-loaded-because-an-unanticipated-error.
3、unrecognized selector sent to instance***(Other link flag)：When a project refer to a static library,the static library concain category,at this time,the category can't be linked,so the error shows:http://my.oschina.net/u/728866/blog/194741。
4、process launch failed: failed to get the task for process 4268：
（1）One is that we are debugging an application which is signed with distribution ad-hoc provision profile.
（2）Another reason is that somehow xcode5 could not find the correct development provision profile although the coding signing identity has the developer signing identity there.
5、The identity used to sign the executable is no longer valid.Please verify that your device’s clock is properly set, and that your signing certificate is not expired. (0xE8008018).：Solutions: