问题
[ Old question title used to be ARC is set to YES, but xcode shows NO, edited in order to make the question clearer.]
I have an iOS project in xcode 4.2.1 using the iOS 5.0 SDK. The project is under version-control (using the built-in git interface), and one of the early commits was after I converted the project to use ARC. Since then all worked OK with some more commits etc.
Now I suddenly notice that the build settings from within xcode shows that the relevant option ("Objective-C Automatic Reference Counting") is set to NO. But when I check the project settings file project.pbxproj directly (either via the version control or just by opening it with a text editor) I see that CLANG_ENABLE_OBJC_ARC is set to YES.
Is this a problem I should worry about? The project compiles and runs OK.
EDIT
As Dondragmer pointed out, there is a separate flag for the project and for the target. Indeed for the project it was set to NO and for the target YES. What does it mean to have a separate flag for the project/target?
回答1:
The question is now apparently: "What does it mean to have a separate flag for the project/target?"
It isn't important unless you have multiple targets in one project. If you do, you can set common settings at the project level. (For instance, the base SDK, or whether ARC is turned on, or which compiler you're using.)
Then, in your targets, set only the few settings that need to be different.
This way, when you do want to change the base SDK, or change the compiler, you can do it in exactly one place, rather than changing every target. This can make large projects much easier to deal with.
来源：https://stackoverflow.com/questions/10058486/what-is-the-meaning-of-separate-settings-for-project-target-in-xcode