_OBJC_IVAR_$_Answer.answer" - objective-c

Question

I have a class that holds number ivars:
// Answer.h
#import <Foundation/Foundation.h>
#interface Answer : NSObject{
#public
int firstNumber;
int secondNumber;
char myOperator;
}
#end
I try to access the code here
numberGroup->firstNumber = arc4random() % 1;
numberGroup->secondNumber = arc4random() % 10;
numberGroup->myOperator = arc4random() % 4;
and I get this error:
Ld
/Users/jack/Library/Developer/Xcode/DerivedData/PowerBuilders-emehzkfcgntrhofxhvurovjmnugn/Build/Products/Debug-iphonesimulator/PowerBuilders.app/PowerBuilders
normal i386
cd "/Users/jack/Desktop/Xcode/Assorted Apps/PowerBuilders"
setenv MACOSX_DEPLOYMENT_TARGET 10.6
setenv PATH "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
-arch i386 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.1.sdk
-L/Users/jack/Library/Developer/Xcode/DerivedData/PowerBuilders-emehzkfcgntrhofxhvurovjmnugn/Build/Products/Debug-iphonesimulator
-F/Users/jack/Library/Developer/Xcode/DerivedData/PowerBuilders-emehzkfcgntrhofxhvurovjmnugn/Build/Products/Debug-iphonesimulator
-filelist /Users/jack/Library/Developer/Xcode/DerivedData/PowerBuilders-emehzkfcgntrhofxhvurovjmnugn/Build/Intermediates/PowerBuilders.build/Debug-iphonesimulator/PowerBuilders.build/Objects-normal/i386/PowerBuilders.LinkFileList
-mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -fobjc-arc -Xlinker -no_implicit_dylibs -D__IPHONE_OS_VERSION_MIN_REQUIRED=50100 -framework UIKit -framework Foundation -framework CoreGraphics -o
/Users/jack/Library/Developer/Xcode/DerivedData/PowerBuilders-emehzkfcgntrhofxhvurovjmnugn/Build/Products/Debug-iphonesimulator/PowerBuilders.app/PowerBuilders
Undefined symbols for architecture i386:
"_OBJC_IVAR_$_Answer.firstNumber", referenced from:
-[ViewController lesson1] in ViewController.o "_OBJC_IVAR_$_Answer.myOperator", referenced from:
-[ViewController lesson1] in ViewController.o "_OBJC_IVAR_$_Answer.secondNumber", referenced from:
-[ViewController lesson1] in ViewController.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with
exit code 1 (use -v to see invocation)

Answer 1

The compiler generates symbol _OBJC_IVAR_$_Answer.firstNumber in the data segment as part of the Answer class metadata when it processes the #implementation section for the Answer class. The data at that symbol is the offset of the firstNumber instance variable within an Answer object.
Either you aren't linking your app with a file that contains an #implementation Answer section, or the compiler hasn't seen the declaration of the firstNumber instance variable before it sees the #implementation Answer section. Check that these are all true:
Answer.m is included in your target's Compile Sources phase.
Answer.m contains an #implementation Answer section.
Answer.m imports Answer.h at the top of Answer.m.