Mixing Objective-C and C++

Question

Hello,

I'm trying to mix together some Objective-C code with C++. I've always heard it was possible, but I've never actually tried it before. When I try to compile the code, I get a bunch of errors. Here's a simple example I've created which illustrates my problems:

AView.h

#import <Cocoa/Cocoa.h>
#include "B.h"

@interface AView : NSView {
    B *b;
}

-(void) setB: (B *) theB;

@end

AView.m

#import "AView.h"

@implementation AView

- (id)initWithFrame:(NSRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code here.
    }
    return self;
}

- (void)drawRect:(NSRect)dirtyRect {
    // Drawing code here.
}

-(void) setB: (B *) theB {
    b = theB;
}

@end

B.h

#include <iostream>

class B {

    B() {
        std::cout << "Hello from C++";
    }

};

Here's the list of errors I get when I try to compile this:

/Users/helixed/Desktop/Example/B.h:1:0 /Users/helixed/Desktop/Example/B.h:1:20: error: iostream: No such file or directory


/Users/helixed/Desktop/Example/B.h:3:0 /Users/helixed/Desktop/Example/B.h:3: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'B'


/Users/helixed/Desktop/Example/AView.h:5:0 /Users/helixed/Desktop/Example/AView.h:5: error: expected specifier-qualifier-list before 'B'


/Users/helixed/Desktop/Example/AView.h:8:0 /Users/helixed/Desktop/Example/AView.h:8: error: expected ')' before 'B'


/Users/helixed/Desktop/Example/AView.m:26:0 /Users/helixed/Desktop/Example/AView.m:26: error: expected ')' before 'B'


/Users/helixed/Desktop/Example/AView.m:27:0 /Users/helixed/Desktop/Example/AView.m:27: error: 'b' undeclared (first use in this function)

All I'm doing to compile this right now is using the default compiler built into Xcode. I didn't edit the Cocoa Application template in any way other than adding the two files I created and chaing the NSView to AView in the xib file. Could somebody please tell me what I'm doing wrong?

Thanks,

helixed

Answer 1

You need to name your .m files .mm. And you will be able to compile C++ code with Objective-C.

So, following your example, your AView.m file should be named AView.mm. It's simple as that. It works very well. I use a lot of std containers (std::vector, std::queue, etc) and legacy C++ code in iPhone projects without any complications.

Answer 2

Never mind, I feel stupid. All you have to do is rename AView.m to AView.mm so the compiler knows it's Objective-C++, and it compiles without a problem.