I was trying to make a sample code run download by the link http://www.magtek.com/support/software/downloads/sw/99510108.zip This is a card reader api ,here is a sample code.When I run this code I got the error: ld: warning: ignoring file /Users/gaurav.garg/Downloads/99510108/SampleCode/Lib/libMTSCRA.a, missing required architecture i386 in file Undefined symbols for architecture i386: "_OBJC_CLASS_$_MTSCRA", referenced from: objc-class-ref in MagTekDemoAppDelegate.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) The class MTSCRA is only a header file,And the solution that I have cheked That we have to add the .m file in compiled source path of build build phase of target...but unfortunately I don't have the MTSCRA.m file.MTscra.h have the AudioToolBox and externalAccesory framework.