This is a newbie C/Objective-C question :-)
Let say I want a CGRectOne and a CGRectTwo constants.
How can I declare that?
Thanks, Jérémy
The other answers are fine -in some cases-.
A) declaring it static
will emit a copy per translation. That is fine if it is visible to exactly one translation (i.e. its definition is in your .m/.c file). Otherwise, you end up with copies in every translation which includes/imports the header with the static definition. This can result in an inflated binary, as well as an increase to your build times.
B) const CGRect CGRectOne = {...};
will emit a symbol in the scope it is declared. if that happens to be a header visible to multiple translations you'll end up with link errors (because CGRectOne
is defined multiple times -- e.g. once per .c/.m file which directly or indirectly includes the header where the constant is defined).
Now that you know the context to use those 2 declarations in, let cover the extern
way. The extern
way allows you to:
The extern
approach is ideal for reusing the constant among multiple files. Here's an example:
File.h
// the declaration in the header:
extern const CGRect CGRectOne;
File.c/m
// the definition:
#import "File.h"
const CGRect CGRectOne = { { 0.0f, 0.0f }, { 1.0f, 1.0f } };
Note: Omitting the const
would just make it a global variable.