1) you’re specifying its linkage. extern linkage allows you or any client to reference the symbol. regarding global variables: if the variable is mutable and/or needs proper construction, then you should consider methods or functions for this object. the notable exception to this is NSString constants: // MONClass.h extern NSString* const MONClassDidCompleteRenderNotification; // MONClass.m NSString* … Read more
The whole and entire purpose of static is to declare that a variable is private to the source file that it is declared in. Thus, it is doing precisely its job in preventing a connection from an extern. Keep in mind that there are four flavors of file-scope variable definition: int blah = 0; — … Read more
You should only use extern template to force the compiler to not instantiate a template when you know that it will be instantiated somewhere else. It is used to reduce compile time and object file size. For example: // header.h template<typename T> void ReallyBigFunction() { // Body } // source1.cpp #include “header.h” void something1() { … Read more
The default storage duration is static, but default linkage is external. You’re not the only one to find it a bit confusing. The C Book (always a good reference) says: “You’ll probably find the interactions between these various elements to be both complex and confusing: that’s because they are!” The section with that quote, Declarations, … Read more
Yes, you can use them together. And yes, it should exactly match the declaration in the translation unit it’s actually declared in. Unless of course you are participating in the Underhanded C Programming Contest 🙂 The usual pattern is: file.h: extern const int a_global_var; file.c: #include “file.h” const int a_global_var = /* some const expression … Read more
If you look in NSObjCRuntime.h (in Foundation) you will see that FOUNDATION_EXPORT compiles to extern in C, extern “C” in C++, and other things in Win32. So, it’s more compatible across languages and operating systems. For many projects, this won’t make any difference.
Introduction There are three forms of declaration of concern here:1 extern int x; // Declares x but does not define it. int x; // Tentative definition of x. int x = 0; // Defines x. A declaration makes an identifier (a name, like x) known. A definition creates an object (such as an int).2 A … Read more
Most recent way (Swift 3; May 2017) to forward declare the enum (NS_ENUM/NS_OPTION) in objective-c is to use the following: // Forward declaration for XYZCharacterType in other header say XYZCharacter.h typedef NS_ENUM(NSUInteger, XYZCharacterType); // Enum declaration header: “XYZEnumType.h” #ifndef XYZCharacterType_h #define XYZCharacterType_h typedef NS_ENUM(NSUInteger, XYZEnumType) { XYZCharacterTypeNotSet, XYZCharacterTypeAgent, XYZCharacterTypeKiller, }; #endif /* XYZCharacterType_h */`
Small correction – for success resolving name by clinet extern “C” must be as on export side as on import. extern “C” will reduce name of proc to: “_GetName”. More over you can force any name with help of section EXPORTS in .def file
Local variables can be declared extern in some cases Let’s read the C99 N1256 standard draft. The standard calls “local variables” as having “block scope”. 6.7.1/5 “Storage-class specifiers” says: The declaration of an identifier for a function that has block scope shall have no explicit storage-class specifier other than extern. Then for what it means … Read more