What are the differences between #import and #include in Objective-C and are there times where you should use one over the other? Is one deprecated?
I was reading the following tutorial: http://www.otierney.net/objective-c.html#preamble and its paragraph about #import and #include seems to contradict itself or at least is unclear.
The #import directive was added to Objective-C as an improved version of #include. Whether or not it's improved, however, is still a matter of debate. #import ensures that a file is only ever included once so that you never have a problem with recursive includes. However, most decent header files protect themselves against this anyway, so it's not really that much of a benefit.
Basically, it's up to you to decide which you want to use. I tend to #import headers for Objective-C things (like class definitions and such) and #include standard C stuff that I need. For example, one of my source files might look like this:
#import <Foundation/Foundation.h>
#include <asl.h>
#include <mach/mach.h>
#include works just like the C #include.
#import keeps track of which headers have already been included and is ignored if a header is imported more than once in a compilation unit. This makes it unnecessary to use header guards.
The bottom line is just use #import in Objective-C and don't worry if your headers wind up importing something more than once.
#include vs #import
History:
#include => #import => Precompiled Headers .pch => @import Module(ObjC); => import Module(Swift)
[Precompiled Headers .pch]
[@import Module(ObjC);]
[import Module(Swift)]
#include + guard == #import
#include guardWiki - macro guard, header guard or file guard prevents to double include a header by a preprocessor that can slow down a build time
#import disadvantage
Works with file scope that is why we have slow build time because a compiler must parse and compile as many times as many .h files were imported in project scope