出現錯誤的情形
像這樣的一大堆，總體說編譯鏈接時錯誤
/Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Products/Debug-iphonesimulator/ClothingOrders.app/ClothingOrders normal i386
cd /Users/JasonSu/Desktop/SVN
setenv IPHONEOS_DEPLOYMENT_TARGET 10.1
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/iPhoneSimulator10.1.sdk -L/Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Products/Debug-iphonesimulator -L/Users/JasonSu/Desktop/SVN/ZBarSDK -F/Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Products/Debug-iphonesimulator -filelist /Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Intermediates/ClothingOrders.build/Debug-iphonesimulator/ClothingOrders.build/Objects-normal/i386/ClothingOrders.LinkFileList -Xlinker -objc_abi_version -Xlinker 2 -fobjc-link-runtime -Xlinker -no_implicit_dylibs -mios-simulator-version-min=6.1 -lz -framework MobileCoreServices -framework SystemConfiguration -framework CFNetwork -framework CoreData -liconv -framework QuartzCore -framework CoreVideo -framework CoreMedia -framework AVFoundation -framework UIKit -framework Foundation -framework CoreGraphics -lzbar -o /Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Products/Debug-iphonesimulator/ClothingOrders.app/ClothingOrders
duplicate symbol _OBJC_METACLASS_$_EntityOrdersTotal in:
/Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Intermediates/ClothingOrders.build/Debug-iphonesimulator/ClothingOrders.build/Objects-normal/i386/EntityOrdersTotal-1502FC93349A1D59.o
duplicate symbol _OBJC_CLASS_$_EntityOrdersTotal in:
/Users/JasonSu/Library/Developer/Xcode/DerivedData/ClothingOrders-bcmqkcjsfgyibbgetgiyczzqcerj/Build/Intermediates/ClothingOrders.build/Debug-iphonesimulator/ClothingOrders.build/Objects-normal/i386/EntityOrdersTotal-1502FC93349A1D59.o
ld: 2 duplicate symbols for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
原因
iOS開發這個錯誤一定少不了，現總結如下，一般是這幾個的問題，如果不是哪你真可麻煩了
1.引用頭文件出錯，把***.h弄成了.m,檢查一下你的所有引用；
2.再就是你引用第三方的庫，你添加文件是系統沒有所第三方庫的.m文件參入的編譯中去，你向項目添加文件得注意了，沒有的要自己添加上；
3.就是不小心添加的重復的類，向Entity之類，具體你可以看這里http://stackoverflow.com/questions/2264455/iphone-duplicate-symbol-error，順便說一下http://stackoverflow.com/這個網站是iOS開發不可少的一個網站；
4.有些frameworks沒有添加進來也會出現上面的問題；
5.這個可能原因而已，比較坑爹，就是你建的類類名極為相似，Xcode識別錯誤，刪掉相似的類重新建或者重命名吧；
6.當第三方文件丟失時，再次拷貝到工程中，有可能造成 .m文件的重復引用，也會出現這類錯誤。
7.引用了別的類沒有在頭文件.h聲明的方法或變量，比如引用了沒有帶關鍵字extern 的靜態變量。
如果發現還有更多的錯誤原因，歡迎留言~
原文參考：查看參考文
