你在哪里声明C的常数？

Where do you declare a constant in objective c?

我在一个头文件const double EARTH_RADIUS=6353;中声明了一个常量，这个常量被导入到其他各种头文件中，得到了一个链接器错误。

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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

基本上，我希望常量可以用于我项目中的所有类。我应该在哪里申报？

您可以在头中声明，并在代码文件中定义它。只需声明为

1	extern const double EARTH_RADIUS;

然后在某个.m文件中(通常是在.m文件中声明的.h文件)

1	const double EARTH_RADIUS = 6353;

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