extern – Page 3 – Tarik Billa

Forward-declare enum in Objective-C

February 3, 2023 by Tarik

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 */`

How to declare constexpr extern?

January 31, 2023 by Tarik

no you can’t do it, here’s what the standard says (section 7.1.5): 1 The constexpr specifier shall be applied only to the definition of a variable or variable template, the declaration of a function or function template, or the declaration of a static data member of a literal type (3.9). If any declaration of a … Read more

What does extern inline do?

December 31, 2022 by Tarik

in K&R C or C89, inline was not part of the language. Many compilers implemented it as an extension, but there were no defined semantics regarding how it worked. GCC was among the first to implement inlining, and introduced the inline, static inline, and extern inline constructs; most pre-C99 compiler generally follow its lead. GNU89: … Read more

using extern template (C++11)

December 2, 2022 by Tarik

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

“FOUNDATION_EXPORT” vs “extern”

November 29, 2022 by Tarik

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.

How do I use extern to share variables between source files?

September 1, 2022 by Tarik

Using extern is only of relevance when the program you’re building consists of multiple source files linked together, where some of the variables defined, for example, in source file file1.c need to be referenced in other source files, such as file2.c. It is important to understand the difference between defining a variable and declaring a … Read more