xcode 将 Objective C 格式的代码转换为纯 C++

Converting Objective C formatted code to pure C++

提问by user436366

I've recently started learning programming to make my own 3D OpenGL game on the iPhone and have made reasonably decent progress so far. I started off using the basic OpenGL example that is provided with the iPhone SDK which helped me get off to a good start. However, as I'm starting to get the hang of things, it has occurred to me that I'm unnecessarily programming in Objective C which will make it harder to port the game to other platforms in the future. So I figured that it would be best to make it properly C++ now to avoid lots of extra work later.

我最近开始学习编程，以便在 iPhone 上制作我自己的 3D OpenGL 游戏，并且到目前为止已经取得了相当不错的进步。我开始使用 iPhone SDK 提供的基本 OpenGL 示例，它帮助我取得了良好的开端。然而，当我开始掌握事情的窍门时，我突然想到我在目标 C 中进行了不必要的编程，这将使未来将游戏移植到其他平台变得更加困难。所以我认为最好现在就使用 C++ 来避免以后的大量额外工作。

To clarify: I'm not actually using any calls to Apple (Objective C) functions or anything, its just that I've based all my clases on the Objective C-style init/dealloc/etc, so that my engine looks like Objective C classes when used. My aim is to replace all the objective C stuff with the C++ equivalents... the trouble is that, being pretty new to C++, I'm not sure what corresponds with what!

澄清一下：我实际上并没有使用任何对 Apple（Objective C）函数或任何东西的调用，只是我的所有类都基于 Objective C 风格的 init/dealloc/etc，所以我的引擎看起来像 Objective使用时的 C 类。我的目标是用 C++ 等价物替换所有目标 C 的东西......问题是，作为 C++ 的新手，我不确定什么对应什么！

Here's a simple example of one of my classes (myLight), in its current Objective C incarnation:

这是我的一个类 (myLight) 的一个简单示例，在其当前的 Objective C 版本中：

//  myLight.h

#import <OpenGLES/EAGL.h>
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>

@interface myLight : NSObject {
    char *name;
    GLfloat *ambient, *diffuse, *specular, *position, *spotDirection;
    GLfloat spotRadius;

    GLfloat *matAmbient, *matDiffuse, *matSpecular;
    GLfloat shininess;
    Byte lightType;
}
@property (readonly) char *name;
@property (assign) GLfloat *position;
@property (assign) GLfloat *spotDirection;

@property (assign) GLfloat *ambient;
@property (assign) GLfloat *diffuse;
@property (assign) GLfloat *specular;

- (id)initWithContentsFromDatastream:(NSData *)fileData;
- (void)set;

@end

And the corresponding .mm file:

以及相应的 .mm 文件：

//  myLight.m

#import "myLight.h"

@implementation myLight
@synthesize name, ambient, diffuse, specular, position, spotDirection;

- (id)initWithContentsFromDatastream:(NSData *)fileData {
    self = [super init];
    NSData *fileContents = fileData;
    uint ptr = 0;

    Byte nameLength;
    [fileContents getBytes:&nameLength range: NSMakeRange(ptr, sizeof(Byte))];
    ptr++;

    name = new char[nameLength];
    [fileContents getBytes:name range: NSMakeRange(ptr, (nameLength * sizeof(char)) )];
    ptr = ptr + (nameLength * sizeof(char) );

    [fileContents getBytes:&lightType range: NSMakeRange(ptr, sizeof(Byte))];
    ptr++;

    position = new GLfloat[4];
    for(int j = 0; j < (4); j++)
        [fileContents getBytes:&position[j] range: NSMakeRange( (j* sizeof(float) ) + ptr, sizeof(float))];
    ptr = ptr + (4 * sizeof(float));

    if(lightType==2){
        spotDirection = new GLfloat[3];
        for(int j = 0; j < (3); j++)
            [fileContents getBytes:&spotDirection[j] range: NSMakeRange( (j* sizeof(float) ) + ptr, sizeof(float))];
        ptr = ptr + (3 * sizeof(float));

        [fileContents getBytes:&spotRadius range: NSMakeRange(ptr, sizeof(float))];
        ptr = ptr + sizeof(float);
    } else 
        spotDirection = NULL;

    diffuse = new GLfloat[4];
    for(int j = 0; j < (4); j++)
        [fileContents getBytes:&diffuse[j] range: NSMakeRange( (j* sizeof(float) ) + ptr, sizeof(float))];
    ptr = ptr + (4 * sizeof(float));

    ambient = new GLfloat[4];
    for(int j = 0; j < (4); j++)
        [fileContents getBytes:&ambient[j] range: NSMakeRange( (j* sizeof(float) ) + ptr, sizeof(float))];
    ptr = ptr + (4 * sizeof(float));

    specular = new GLfloat[4];
    for(int j = 0; j < (4); j++)
        [fileContents getBytes:&specular[j] range: NSMakeRange( (j* sizeof(float) ) + ptr, sizeof(float))];
    ptr = ptr + (4 * sizeof(float));

    [self set];

  return self;
}

- (void)set{
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
    glLightfv(GL_LIGHT0, GL_SPECULAR, specular);
    glLightfv(GL_LIGHT0, GL_POSITION, position);

    if(lightType==2)
        glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spotDirection);
}

- (void)dealloc {
    delete[] specular;
    delete[] ambient;
    delete[] diffuse;

    if (spotDirection)
        delete[] spotDirection;

    delete[] position;
    delete[] name;

    [super dealloc];
}

@end

If someone could point out which lines need to be changed and, more importantly, what they should be changed to to make it compile as pure C++, I'd really appreciate it.

如果有人可以指出需要更改哪些行，更重要的是，应该将它们更改为哪些行以使其编译为纯 C++，我将不胜感激。

Many Thanks!

非常感谢！

回答by Alfonso

First of all, please keep in mind that Objective-C is not just a "different format" of C, it's a separate language and more important, in the case of Cocoa, a separate framework. Therefore if you want to be able to port your project to other platforms in the future, you not only have to get rid of Objective-C but also of the Cocoa framework.

首先，请记住，Objective-C 不仅仅是 C 的“不同格式”，它是一种独立的语言，更重要的是，在 Cocoa 的情况下，它是一个独立的框架。因此，如果您希望将来能够将您的项目移植到其他平台，您不仅要摆脱 Objective-C，还必须摆脱 Cocoa 框架。

To map the classes from Objective-C to C++ you would have to do the following:

要将类从 Objective-C 映射到 C++，您必须执行以下操作：

• create a new C++ class to replace the old class
• create constructors for the -init...methods
• create a destructor for the -deallocmethod
• create other methods which duplicate the functionality
• for properties you would probably create getters and setters instead
• replace the #importwith #includedirectives, as this directive only exists in Objective-C (make sure that the headers you include are protected against multiple includes)
• get rid of usages of NS... classes and methods, as those are part of the Cocoa framework and most probably cannot be ported

• 创建一个新的 C++ 类来替换旧的类
• 为-init...方法创建构造函数
• 为-dealloc方法创建析构函数
• 创建其他复制功能的方法
• 对于属性，您可能会创建 getter 和 setter
• 替换#importwith#include指令，因为该指令仅存在于 Objective-C 中（确保您包含的标头受到保护以防止多个包含）
• 摆脱 NS... 类和方法的使用，因为它们是 Cocoa 框架的一部分，很可能无法移植

You should take some time to consider how you will use the code you're writing. Porting 1:1 is probably not such a great idea as there are many differences in idioms between coding in Cocoa and C++ (or any other language/framework).

您应该花一些时间考虑如何使用正在编写的代码。移植 1:1 可能不是一个好主意，因为 Cocoa 和 C++（或任何其他语言/框架）中的编码之间的习语存在很多差异。

回答by dreamlax

Most of the applications logic may be translatable to C++, but there are going to be things that have no straightforward equivalent in C++. For example:

大多数应用程序逻辑可能可以翻译成 C++，但有些东西在 C++ 中没有直接的等价物。例如：

1. There is no @encode()compiler directive (which is used for NSValue and a few other classes).
2. There is no straightforward equivalent to doesNotRecognizeSelector:, respondsToSelector:, conformsToProtocol:or performSelector:(and other methods of similar nature).
3. In Objective-C it is fine to send a message to nil, but in C++ it is not OK to call a member function on a null pointer.
4. Objective-C allows extending existing classes using class categories, for example, you can add a method to NSStringwhich counts the number of spaces, called numberOfSpacesand it will be available for all NSStringinstances in your application.
5. C++ does not have a finallyblock for try/catch, but Objective-C has @finallyfor @try/@catch.

1. 没有@encode()编译器指令（用于 NSValue 和一些其他类）。
2. 没有直接等同于doesNotRecognizeSelector:、respondsToSelector:、conformsToProtocol:或performSelector:（以及其他类似性质的方法）。
3. 在 Objective-C 中，可以向 发送消息nil，但在 C++ 中，在空指针上调用成员函数是不行的。
4. Objective-C 允许使用类类别扩展现有类，例如，您可以添加一个NSString计算空格数的方法，调用numberOfSpaces该方法可用于NSString应用程序中的所有实例。
5. C++ 没有finally用于try/的块catch，但 Objective-C 有@finally用于@try/ @catch。

If you plan on releasing your application to multiple platforms, what you could do is try to abstract as much as you can into a separate library. Your iPhone application can be written in Objective-C and use functions from your library, and if you plan on porting it to another system whose frameworks require C++, then you can write a C++ application and use the same functions from the same library. I imagine your library would basically consist of [at least] your drawing routines and core game engine logic.

如果您计划将您的应用程序发布到多个平台，您可以做的是尝试将尽可能多的内容抽象到一个单独的库中。您的 iPhone 应用程序可以用 Objective-C 编写并使用库中的函数，如果您计划将其移植到框架需要 C++ 的另一个系统，那么您可以编写 C++ 应用程序并使用来自同一库的相同函数。我想你的库基本上由[至少]你的绘图程序和核心游戏引擎逻辑组成。