问题
What do static, extern and inline (and their combinations) mean in Objetive-C using the LLVM compiler?
Also, I noticed that there are CG_EXTERN and CG_INLINE macros. Should we be using those instead?
(I couldn't find a source with a clear explanation so I thought it might be useful to create one here, or point to it if someone knows one)
回答1:
What do static, extern and inline (and their combinations) mean in Objetive-C using the LLVM compiler?
The same as in C, unless you compile as ObjC++ -- then they mean the same as found in C++.
So here is an introduction for C, but read the links if you are ready to use these because the details are important:
Extern
Summary: Indicates that an identifier is defined elsewhere.
Details: http://tigcc.ticalc.org/doc/keywords.html#extern
Static
Summary (value): Preserves variable value to survive after its scope ends.
Summary (function): Effectively emits unnamed copies - useful for private functions in C, and can be used to escape multiple definition errors when used with inline functions.
Details: http://tigcc.ticalc.org/doc/keywords.html#static
Inline
Summary: Suggests the body of a function should be moved into the callers.
Details: http://tigcc.ticalc.org/doc/gnuexts.html#SEC93
Note that inline and static are quite a bit more complex in C++ (like pretty much everything in C++).
I also found that there are CG_EXTERN and CG_INLINE macros. Should we be using those instead?
No.
Instead, you should specify your own, with your own meanings, if you need this type of functionality. CG_EXTERN and CG_INLINE have specific meanings (which may change), and are meant to be used in their defined context -- also, you don't want to have to include a whole handful of frameworks (all CoreGraphics/ApplicationServices/CoreFoundation/etc.) when you want to specify something is extern in a way that works in C and C++.
回答2:
Justin covered most of it, but I found some other nice resources for those who want to dig deeper:
By declaring a function inline you tell the compiler to replace the complete code of that function directly into the place from where it was called. This is a rather advanced feature that requires understanding of lower-level programming.
Inline functions
This SO question has an enormous answer about extern variables - variables defined "somewhere else" - but need to be used also "here".
Static preserves variable life outside of scope. The Variable is visible within the scope it was declared.
What does a static variable mean?
来源：https://stackoverflow.com/questions/11985307/static-extern-and-inline-in-objective-c