Using C++ classes in Objective - C

Question

I am trying to use some C++ classes in my Objective-C code for an iPhone application. I am just trying to declare the C++ object, and I am running into problems. Even though I am declaring the C++ header file in the Objective-C class I want to use it in, it does not appear that my Objective-C recognizes the C++ object. Here is my Objective-C code:

 //implementation file
#import "CPPClass.h"

@implementation MyViewController
- (void) viewDidLoad
{
    CPPClass object;
}

but I get an "Use of undeclared identifier 'CPPClass'" warning.

How am I supposed to do this?

And, technically, you should #include C/C++ header files since some may actually rely on the difference in behaviour between #include and #import. Though you can be pretty certain that's making no difference here so this is in no way intended as an answer. — Tommy
– Tommy, Commented Jan 16, 2012 at 20:16
@Tommy that is not the case, check out this question here for clarification. Using #import increases performance, with no drawbacks. — Richard J. Ross III
– Richard J. Ross III, Commented Jan 16, 2012 at 20:20
@RichardJ.RossIII the two differ in behaviour or they wouldn't have added #import in the first place. So all C/C++ headers are written against the #include behaviour. See e.g. user512705's answer to the question you linked to for an example of where substituting #import for #include breaks a program. — Tommy
– Tommy, Commented Jan 16, 2012 at 20:43
@Tommy no, you are missing the point. The only difference between #include and #import is that #import checks to see if the file has been included before, and if it has, it doesn't include it, reducing compile time, with no side-affects. — Richard J. Ross III
– Richard J. Ross III, Commented Jan 16, 2012 at 20:45

DHamrick · Accepted Answer · 2012-01-16 20:15:15Z

6

If you want to use C++ code in Objective-C you need to have it in files with the .mm extension, which the compiler will interpret as Objective-C++ code. You also should #include C++ headers, not #import them.

answered Jan 16, 2012 at 20:15

DHamrick

8,5389 gold badges49 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Richard J. Ross III Over a year ago

#include vs #import means nothing really. You can do either. #import only checks to see if you haven't included the file already

Hot Licks Over a year ago

And, rather than changing to .mm, you can set the Objective-C++ file type in the file attributes.

Collectives™ on Stack Overflow

Using C++ classes in Objective - C

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related