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This article will explain in detail what common macros are about iOS. The editor thinks it is very practical, so I share it with you for reference. I hope you can get something after reading this article.

FOUNDATION_EXPORT, UIKIT_EXTERN

The macro works like extern and works similarly to extern. In the .m file, the definition is as follows

NSString * const kFoundationExportString = @ "Hello World"; NSString * const kExternString = @ "Hello World"

You can then access the constant in the class that imported the .h file by adding the following declaration to the .h file.

FOUNDATION_EXPORT NSString * const kFoundationExportString; extern NSString * const kExternString

If you want to access these two constants in a class that does not import the .h file, you should put the above code in the .m file of the class.

UIKIT_EXTERN only adds compatibility compared to extern, using the same method.

The use is as follows:

NSString * str = @ "Hello World"; if (str = = kConstantString) {NSLog (@ "equal");}

String constants declared with FOUNDATION_EXPORT compare the address of the pointer, while constant strings defined by the # define macro can only be compared using isEqualToString, which is more efficient.

Comparison between define and FOUNDATION_EXPORT

NS_STRING_ENUM and NS_EXTENSIBLE_STRING_ENUM

These two macro definitions are used for bridging Swift for Objective-C, and their purpose is to enumerate extensions when bridged to Swift, using the following:

Declare in the .h file

Typedef NSString * ViewControllerKey NS_STRING_ENUM; FOUNDATION_EXPORT ViewControllerKey const ViewControllerKeyTitle; FOUNDATION_EXPORT ViewControllerKey const ViewControllerKeySubtitle; FOUNDATION_EXPORT ViewControllerKey const ViewControllerKeySummary

Defined in the .m file:

ViewControllerKey const ViewControllerKeyTitle = @ "title"; ViewControllerKey const ViewControllerKeySubtitle = @ "subtitle"; ViewControllerKey const ViewControllerKeySummary = @ "summary"

Use the following in the swift file:

Print ("\ (ViewControllerKey.title)\ (ViewControllerKey.subtitle)\ (ViewControllerKey.summary)")

The difference between these two macro definitions is that NS_STRING_ENUM is deterministic, NS_EXTENSIBLE_STRING_ENUM is extensible, and can also be extended in swift.

_ _ VA_ARGS__

# # is an adhesive that binds the front and rear parts together, which means "character".

The _ _ VA_ARGS__ will be replaced by the argument list in the precompilation. Represents a list of variable parameters.

The function of adding # # before the # # _ _ VA_ARGS__ macro is that when the number of variable parameters is 0, the # # here plays the role of removing the previous redundant ones, otherwise there will be compilation errors.

# define BLOCK_EXEC (block,...) If (block) {block (_ _ VA_ARGS__);}; # ifdef DEBUG # define LogInfo (s,...) NSLog (@ "[LogInfo]% @", [[NSString stringWithUTF8String:__FILE__] lastPathComponent], _ _ LINE__, [NSString stringWithFormat: (s), # # _ VA_ARGS__]) # else # define LogInfo (s,...) # endif

This is the end of this article on "what are the common macros in iOS?". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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