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Calling Objective C code within C++ using Cocoa

Started by FruitJuice27 Nov 24, 2004 at 6:32 PM 11 replies 5.4k views

Original Post

Nov 24, 2004 at 6:32 PM

Is it possible to call Obj-C code inside C++ code? How would I go about this? For instance i have a MessageBox.cpp that uses the windows MessageBox function if copiling for windows. I would like it to Compile for MAC using the Cocoa NSAlert. I am doing: #if WINDOWS #elif MAC #endif Thanks :)

igni ferroque

Nov 24, 2004 at 10:36 PM

You should be able to use the syntax directly using Objective-C++ (basically Objective-C ∪ C++). See this site for details.

Qw3r7yU10p!

Nov 25, 2004 at 12:22 AM

See this thread:
Portability (#ifdef considered harmful)

FruitJuice27

Author

FruitJuice27

Nov 25, 2004 at 10:45 AM

Thankyou for both your replies!

Petewood - I will keep in mind the swiss cheese code that can come with #ifdef and try to use it correctly. I am staying away from OS API as much as possible (using SDL and OpenGL) so I think that it will be ok for now.

igni - Thanks for the link to that article. It is exactly what I need to solve my issue.

Qw3r7yU10p!

Nov 25, 2004 at 11:25 AM

Quote:
Original post by FruitJuice27
Thankyou for both your replies!

No problem.

FruitJuice27

Author

FruitJuice27

Nov 25, 2004 at 11:50 AM

I am not quite understanding Xcode Frameworks. I have added the Appkit framework to my project so that I could use NSAlert.

However my Compiler says that NSAlert is undefined.

NSAlert *alert = [[[NSAlert alloc] init] autorelease];

Is it because im doing something wrong with mixing ObjC and C++? This is a C++ file and is mostly C++ code except for this.

chollida1

Nov 25, 2004 at 11:59 AM

are you importing the framework correctly. We build our apps on C++ code that is shared between the PC and MAC. with the mac app written in Objective C code. We have no problems with it.

Error's like this are ususally from fortetting to import a header. or linking to the wrong framework

Cheers
Chris

FruitJuice27

Author

FruitJuice27

Nov 25, 2004 at 12:10 PM

Thanks Chris. I did not understand that adding a framework wasnt all I needed. You are right that I was missing the proper headers.

For this to work I also had to change to .mm extention.

chollida1

Nov 25, 2004 at 12:51 PM

Oh yes, I should have reminded you about the .mm extension. I always found it "hacky" that apple would compile a file based on its extension, while the whole OS does its best to sheild the user from the extention of a file.

Glad you got it to work.

Cheers
Chris

FruitJuice27

Author

FruitJuice27

Nov 25, 2004 at 1:46 PM

Since the extention must be .mm, and my VC++6 wants .cpp, I guess I need different files for each compiler?

I was hoping to have only one file and use:
#if WINDOWS
#elif MAC
#endif

Is there a way to embedd the obj-C code in the cpp file so I can use it with VC++6?

Mabe the best solution is to have two files? What do you do Chris?

[Edited by - FruitJuice27 on November 25, 2004 2:46:05 PM]

igni ferroque

Nov 25, 2004 at 3:59 PM

Quote:
Original post by chollida1
Oh yes, I should have reminded you about the .mm extension. I always found it "hacky" that apple would compile a file based on its extension, while the whole OS does its best to sheild the user from the extention of a file.

This is standard GCC behavior but you can get around it with certain flags.

Quote:
For instance i have a MessageBox.cpp that uses the windows MessageBox function if copiling for windows. I would like it to Compile for MAC using the Cocoa NSAlert.

Create a C/C++ interface for creating a message box, then create two implementation files. One will be an .mm and one will be a .cpp. You can then set up your project so that the Windows version compiles and links with the the Windows implementation and the MacOS version compiles and links with the Mac implementation. Your code calls the wrapper function. No #ifdefs necessary.

chollida1

Nov 25, 2004 at 4:36 PM

We use .mm. Vs.net will compile .mm file if you set up a file association for them. Just look in the registry for .cpp and copy that key for .mm.

Works well for us. igni ferroque mentioned that you can use certain compiler flags to get cpp files to work as ObjectiveC++ files but we've never had any luck getting it to work by setting the compile as ObjectiveC++ flag.

And judging by the XCode mailing list we aren't alone

Cheers
Chris

FruitJuice27

Author

FruitJuice27

Nov 25, 2004 at 4:43 PM

Thanks for the advice. Since im going to the extra trouble to write for both platforms, I might as well bite the bullet and do two files.

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