Question

I’m trying to create a library in C++ in XCode, and I’m trying to use it inside an iPhone project. I’m using XCode 4.3.2. Since there’s no ready template available in iOS development to create a C++ library, I’m using the Mac OSX – Framework & Library -> C/C++ Library option.

In this project, I’m having .h and .cpp files. I purposely want to keep my C++ code in .cpp files since it may later be used on Android or Windows 8. In order for it to link against a sample iPhone project, I’ve modified the project’s target to point to Latest SDK iOS 5.1, and use the architecture armv6 and armv7.

Following is my .h file

#ifndef Test_Test_h
#define Test_Test_h
class Test {   --> I get the error here saying unknown type 'class'; did you mean 'Class'?

public:
Test();
~Test();
int addTwoNums(int a, int b);
};


#endif

Following is my .cpp file in my C++ library

#include <iostream>
#include "Test.h"
Test::Test(){}
Test::~Test(){}
int Test::addTwoNums(int a, int b)
{
return (a + b);
}

Now in order to enable function calls from within my iPhone project, I’ve created a wrapper layer embedding C++ objects inside a .mm class courtesy this article:
http://www.philjordan.eu/article/mixing-objective-c-c++-and-objective-c++

Following is the implementation of my wrapper header file which is part of my separate iPhone project

#import <Foundation/Foundation.h>
@interface TestWrapper : NSObject
-(id)init;
-(int)returnSumFromCpluspus:(int) a b:(int) b;
@end

Following is the implementation of my wrapper .mm file part of my separate iPhone

#import "TestWrapper.h"
#import "Test.h"
@implementation testWrapper
{
Test *tst;
}

-(id) init
{
self = [super init];
    if (self) {
    tst = new tst();
    if(!tst)
        self = nil;
}
return self;
}

-(int)returnSumFromCpluspus:(int) a b:(int)b
{
int result = 0;
if(tst)
    result = tst->addTwoNums(a,b);
return result;
}

- (void)dealloc
{   
 if(tst)
 delete tst;
}
@end

Now in my iPhone project, I’ve linked it against this static library. I’m able to compile and debug just fine only when I select a “compile sources as: Objective-C++” in my iPhone project’s target, and not my C++ static library project. If I change the compile sources as: According to the File Type”, I get compilation errors:

unknown type name ‘class’;did you mean ‘Class’?
Expected ‘;” after top level decorator.

My question is it compulsory to change my iPhone project property target compilation type as Objective-C++, and not my static library C++ project or is there another way, which I might be missing and not aware of?

Any help in this regard will be greatly appreciated!

Thanks,
Asheesh

Answer 1

It would help us understand your problem if you edit your question to include some of the actual source code that the compiler doesn’t like.

That said, I think you are trying to #include (or #import) a .h file containing C++ class definitions in a .m file.

A .m file is (by default) an Objective-C file, not an Objective-C++ file, so the compiler will reject C++ constructs in a .m file. If a .m file includes/imports a .h file, that .h file must also contain only Objective-C code – not C++ or Objective-C++ code.

You say that you have written a wrapper layer using Objective-C++. So you probably have a file named something like Wrapper.h that declares the @interface of your wrapper class, and you have a Wrapper.mm containing the @implementation (in Objective-C++) of the wrapper class.

You need to make sure that Wrapper.h contains no C++ code. It can only contain Objective-C, because you are going to include/import Wrapper.h in your .m files.

If your Wrapper.h includes/imports a header file from your C++ library, you need to take that out. You can only include your C++ library header files directly in your .mm files, or in other .h files that you only include from .mm files.