在Cocoa项目中使用C ++类时，找不到标准C ++包含 [英] Can't find standard C++ includes when using C++ class in Cocoa project

问题描述

我有一个Cocoa项目（Mac OS X应用程序），所有的Objective-C。我从一个C ++类（我知道工程）从另一个项目，并为它做一个Objective-C包装。 ObjC包装类使用.mm扩展名。但是，C ++头文件包含 #include 到标准C ++头文件（例如< vector> ，我得到的错误。

I have a Cocoa project (a Mac OS X app), all Objective-C. I pulled in one C++ class (which I know works) from another project, and make an Objective-C wrapper for it. The ObjC wrapper class is using a .mm extension. However, the C++ header file contains #includes to standard C++ header files (<vector>, for example), and I get errors on those.

一个最小示例如下所示。 CppClass是C ++类，CppWrapper是包装它的ObjC类。

A minimal example would look like the following. CppClass is the C++ class, and CppWrapper is the ObjC class which wraps it.

//  CppClass.h
#ifndef _CPP_CLASS_H_
#define _CPP_CLASS_H_

#include <vector>

class CppClass
{
public:
    CppClass() {}
    ~CppClass() {}

private:
    std::vector<int> my_ints;
};
#endif /* _CPP_CLASS_H_ */

//  CppWrapper.h
#import <Foundation/Foundation.h>
#import "CppClass.h"

@interface CppWrapper : NSObject {
    CppClass* myCppClass;
}
@end

//  CppWrapper.mm
#import "CppWrapper.h"

@implementation CppWrapper

- (id)init
{
    self = [super init];
    if (self) {
        myCppClass = new CppClass;
    }    
    return self;
}

- (void)dealloc
{
    delete myCppClass;

    [super dealloc];
}

@end

// The file that uses CppWrapper
//  TestAppDelegate.m

#import "TestAppDelegate.h"
#import "CppWrapper.h"

@implementation TestAppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    myWrapper = [[CppWrapper alloc] init];
}
@end

我得到的错误是<$ cppClass.h中的向量的c $ c> #include 错误是

The error I'm getting is the #include of vector in CppClass.h. The error is

词汇或预处理器问题：'vector' / p>

lexical or Preprocessor issue: 'vector' file not found

此代码在另一个（所有C ++）项目中正常工作，因此我确信它是一个构建设置，在包装类中做错了。我使用Xcode 4.我创建了一个默认的Cocoa Mac OS应用程序项目，所有设置都是默认的。

This code works fine in another (all C++) project, so I'm pretty sure it's a build setting, or something I've done wrong in the wrapper class. I'm using Xcode 4. I created a default Cocoa Mac OS app project and all settings are default.

更新：我刚刚意识到如果我将TestAppDelegate的文件类型设置为Objective-C ++（或重命名为TestAppDelegate.mm），它的工作原理。我不明白的是，这个类是纯Objective-C;为什么它必须被编译为Objective-C ++？在我的C ++类上有一个Objective-C包装器的整个要点是，我不必将整个项目构建为Objective-C ++。

Update: I just realized that if I set TestAppDelegate's File Type to Objective-C++ (or rename it to TestAppDelegate.mm), it works. What I don't understand is, this class is pure Objective-C; why does it have to be compiled as Objective-C++? The whole point of having an Objective-C wrapper on my C++ class is so that I don't have to build the entire project as Objective-C++.

推荐答案

CppWrapper 类的问题是它不提供纯粹的Objective-C接口。在你的 CppWrapper.h 文件中，你正在导入C ++类的头文件，这意味着任何导入包装类的Objective-C类都需要被编译为Objective -C ++，包括你的 TestAppDelegate 。

The problem with your CppWrapper class is that it doesn't present a pure Objective-C interface. In your CppWrapper.h file, you're importing the C++ class's header file, which means that any Objective-C class that imports the wrapper class will need to be compiled as Objective-C++, including your TestAppDelegate.

相反，你需要这样做完全隐藏 CppWrapper.mm 文件中的C ++：

Instead, you'd need to do something like this to completely hide the C++ within the CppWrapper.mm file:

//  CppWrapper.h
#import <Foundation/Foundation.h>

@interface CppWrapper : NSObject {
    void *myCppClass;
}
- (void)doSomethingWithCppClass;
@end


//  CppWrapper.mm
#import "CppWrapper.h"
#import "CppClass.h"

@implementation CppWrapper

- (id)init {
    self = [super init];
    if (self) {
        myCppClass = new CppClass;
    }    
    return self;
}

- (void)dealloc {
    delete myCppClass;
    [super dealloc];
}

- (void)doSomethingWithCppClass {
   static_cast<CppClass *>(myCppClass)->DoSomething();
}

@end

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