在Objective-C++中使用C++类

Question

我在Cocoa应用程序中使用一个小的C++库(atm只是一个非常简单的例子来学习我应该怎么做).

所以我在命名空间中有一个小的C++类,如下所示:

namespace testlib {
class Test {
public:
    Test(unsigned a);
    Test operator+(const Test& other) const;
    Test operator+(unsigned other) const;
    Test& operator+=(unsigned other);
    Test& operator+=(const Test& other);
    unsigned getValue() const;
private:
    unsigned theValue;
};
}

然后我有一个带有以下代码的.h文件:

#import <Foundation/Foundation.h>
#import "testlib.h"

@interface test : NSObject {
     testlib::Test* testClass;
}

- (id)init;
- (id)add: (unsigned)value;
- (unsigned)value;
- (void)dealloc;

@property void* testClass;

@end

最后一个实现(在一个名为test.mm的文件中):

#import "test.h"

@implementation test

@synthesize testClass;

- (id)init {
 testClass = new testlib::Test(0);
 return self;
}

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

- (id)add: (unsigned)value {
 *testClass += value;
 return self;
}

- (unsigned)value {
     return testClass->getValue();
}

当我尝试编译它时,我得到以下错误:

CompileC build/testipod.build/Debug-iphonesimulator/testipod.build/Objects-normal/i386/WindowController.o WindowController.m normal i386 objective-c com.apple.compilers.gcc.4_2
 cd /Users/sausalito/eth/testipod
 setenv LANG en_US.US-ASCII
 setenv PATH "/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/gcc-4.2 -x objective-c -arch i386 -fmessage-length=0 -pipe -std=c99 -Wno-trigraphs -fpascal-strings -fasm-blocks -O0 -Wreturn-type -Wunused-variable -D__IPHONE_OS_VERSION_MIN_REQUIRED=30000 -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.3.sdk -fvisibility=hidden -mmacosx-version-min=10.5 -gdwarf-2 -iquote /Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/testipod-generated-files.hmap -I/Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/testipod-own-target-headers.hmap -I/Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/testipod-all-target-headers.hmap -iquote /Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/testipod-project-headers.hmap -F/Users/sausalito/eth/testipod/build/Debug-iphonesimulator -F/Users/sausalito/eth/testipod/../testlib/build -I/Users/sausalito/eth/testipod/build/Debug-iphonesimulator/include -I/Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/DerivedSources/i386 -I/Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/DerivedSources -include /var/folders/4f/4fSYMOmtHHSRoBf+XVFQ+k+++TM/-Caches-/com.apple.Xcode.502/SharedPrecompiledHeaders/testipod_Prefix-cwdputxcxpofoydkulngkdplqxbt/testipod_Prefix.pch -c /Users/sausalito/eth/testipod/WindowController.m -o /Users/sausalito/eth/testipod/build/testipod.build/Debug-iphonesimulator/testipod.build/Objects-normal/i386/WindowController.o

 In file included from /Users/sausalito/eth/testipod/Classes/test.h:10,
             from /Users/sausalito/eth/testipod/WindowController.m:10:
/Users/sausalito/eth/testipod/Classes/testlib.h:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'testlib'
 In file included from /Users/sausalito/eth/testipod/WindowController.m:10:
/Users/sausalito/eth/testipod/Classes/test.h:13: error: expected specifier-qualifier-list before 'testlib'

/Users/sausalito/eth/testipod/Classes/test.mm:13:0 /Users/sausalito/eth/testipod/Classes/test.mm:13: error: type of property 'testClass' does not match type of ivar 'testClass'

我究竟做错了什么？？看起来它使用C编译器来编译头文件.

当我将成员声明为void*类型然后在实现中使用强制转换时,我可以将它包装在Objective-C类中.但这绝对不是最舒服的做法.

Answer 1

重命名你WindowController.m的WindowController.mm.

如果文件名是.m,则整个"翻译单元"将在没有++的ObjC中编译.但是,在您test.h的导入testlib.h中,您正在导入包含C++代码的内容.这些C++代码在C中无效,从而导致编译器错误.

顺便说一句,

- (id)init {
 testClass = new testlib::Test(0);
 return self;
}

你应该调用super的init:

- (id)init {
  if ((self = [super init]))
     testClass = new testlib::Test(0);
  return self;
}

该物业

@property void* testClass;

应该返回测试*.

@property(readonly,assign) testlib::Test* testClass;