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I declared a constant in a header file const double EARTH_RADIUS=6353; that is imported to various other headers and I got a linker error.
Ld /Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Products/Debug-iphonesimulator/BadgerNew.app/BadgerNew normal i386 cd /Users/Teguh/Dropbox/badgers/BadgerNew setenv MACOSX_DEPLOYMENT_TARGET 10.6 setenv PATH "/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin" /Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/llvm-g++-4.2 -arch i386 -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator4.3.sdk -L/Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Products/Debug-iphonesimulator -F/Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Products/Debug-iphonesimulator -filelist /Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Intermediates/BadgerNew.build/Debug-iphonesimulator/BadgerNew.build/Objects-normal/i386/BadgerNew.LinkFileList -mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -framework CoreLocation -framework UIKit -framework Foundation -framework CoreGraphics -framework CoreData -o /Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Products/Debug-iphonesimulator/BadgerNew.app/BadgerNew ld: duplicate symbol _EARTH_RADIUS in /Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Intermediates/BadgerNew.build/Debug-iphonesimulator/BadgerNew.build/Objects-normal/i386/NearbyIsiKota.o and /Users/Teguh/Library/Developer/Xcode/DerivedData/BadgerNew-bjopcgcgsjkcvcevflfbvsjwfgnu/Build/Intermediates/BadgerNew.build/Debug-iphonesimulator/BadgerNew.build/Objects-normal/i386/FrontPageofBadger.o for architecture i386 collect2: ld returned 1 exit status Basically I want the constant to be available for all classes on my project. Where should I declare it?
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You use the Const statement to declare a constant and set its value. By declaring a constant, you assign a meaningful name to a value. Once a constant is declared, it cannot be modified or assigned a new value. You declare a constant within a procedure or in the declarations section of a module, class, or structure.
Constants are basically variables whose value can't change. In C/C++, the keyword const is used to declare these constant variables. In Java, you use the keyword final .
#define name value , however, is a preprocessor command that replaces all instances of the name with value . For instance, if you #define defTest 5 , all instances of defTest in your code will be replaced with 5 when you compile. Follow this answer to receive notifications.
You can declare in the header, define it in a code file. Simply declare it as
extern const double EARTH_RADIUS; then in a .m file somewhere (usually the .m for the .h you declared it in)
const double EARTH_RADIUS = 6353; There are two ways to accomplish this:
1st option- As previous replies pointed, in the .h file:
myfile.h extern const int MY_CONSTANT_VARIABLE; and in myfile.m define them
myfile.m const int MY_CONSTANT_VARIABLE = 5; 2nd option- My favourite:
myfile.h static const int MY_CONSTANT_VARIABLE = 5 ; If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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