我有一个昨天建立并运行的项目，但今天它没有链接。我什么都没改变。我不知道是什么原因引起的。我没有看到它所指的main.o和_main。有任何想法吗？我尝试了干净和构建。我看了几个关于这个网站的东西，但没有看到任何让我感到满意的东西。
Ld /Users/michelecleary/Library/Developer/Xcode/DerivedData/Hackbook-dpdqkbplprywqfeflsbqlgpwbioo/Build/Products/Debug-iphonesimulator/Hackbook.app/Hackbook normal i386
cd /Users/michelecleary/fbPic2/facebook-ios-sdk/sample/Hackbook
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/iPhoneSimulator5.0.sdk -L/Users/michelecleary/Library/Developer/Xcode/DerivedData/Hackbook-dpdqkbplprywqfeflsbqlgpwbioo/Build/Products/Debug-iphonesimulator -F/Users/michelecleary/Library/Developer/Xcode/DerivedData/Hackbook-dpdqkbplprywqfeflsbqlgpwbioo/Build/Products/Debug-iphonesimulator -filelist /Users/michelecleary/Library/Developer/Xcode/DerivedData/Hackbook-dpdqkbplprywqfeflsbqlgpwbioo/Build/Intermediates/Hackbook.build/Debug-iphonesimulator/Hackbook.build/Objects-normal/i386/Hackbook.LinkFileList -mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -Xlinker -no_implicit_dylibs -D__IPHONE_OS_VERSION_MIN_REQUIRED=40000 -o /Users/michelecleary/Library/Developer/Xcode/DerivedData/Hackbook-dpdqkbplprywqfeflsbqlgpwbioo/Build/Products/Debug-iphonesimulator/Hackbook.app/Hackbook
Undefined symbols for architecture i386:
"_objc_msgSend", referenced from:
_main in main.o
-[HackbookAppDelegate application:didFinishLaunchingWithOptions:] in HackbookAppDelegate.o
-[HackbookAppDelegate applicationDidBecomeActive:] in HackbookAppDelegate.o
-[HackbookAppDelegate application:handleOpenURL:] in HackbookAppDelegate.o
-[HackbookAppDelegate application:openURL:sourceApplication:annotation:] in HackbookAppDelegate.o
-[HackbookAppDelegate dealloc] in HackbookAppDelegate.o
-[RootViewController dealloc] in RootViewController.o
...
"_UIApplicationMain", referenced from:
_main in main.o
"_OBJC_CLASS_$_NSAutoreleasePool", referenced from:
objc-class-ref in main.o
"_NSLog", referenced from:
-[HackbookAppDelegate applicationDidBecomeActive:] in HackbookAppDelegate.o
-[RootViewController fbDidExtendToken:expiresAt:] in RootViewController.o
-[RootViewController request:didFailWithError:] in RootViewController.o
-[APICallsViewController apiGraphUserPhotosPost] in APICallsViewController.o
-[APICallsViewController request:didFailWithError:] in APICallsViewController.o
-[APICallsViewController dialogCompleteWithUrl:] in APICallsViewController.o
-[APICallsViewController dialogDidNotComplete:] in APICallsViewController.o
...