将Objective C格式的代码转换为纯C ++

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,在iPhone上制作我自己的3D OpenGL游戏,到目前为止已取得了相当不错的进展。我开始使用随iPhone SDK提供的基本OpenGL示例,这帮助我开始了一个良好的开端。然而,当我开始掌握一些事情时,我发现我在Objective C中进行了不必要的编程,这将使得将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正确地使用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)函数或其他任何函数的调用,只是因为我将所有的条款都基于Objective C风格的init / dealloc / etc,所以我的引擎看起来像Objective使用C类时。我的目标是用C ++等价物替换所有目标C的东西...麻烦的是,对于C ++来说是新手,我不确定什么对应于什么!

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)的简单示例,在其当前的Objective C化身中:

//  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:

和相应的.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.

如果有人可以指出哪些行需要更改,更重要的是,应该将它们更改为使其编译为纯C ++,我真的很感激。

Many Thanks!

2 个解决方案

#1

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”,它是一种单独的语言,更重要的是,在Cocoa的情况下,它是一个单独的框架。因此,如果您希望将来能够将项目移植到其他平台,您不仅需要摆脱Objective-C,还需要摆脱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

创建一个新的C ++类来替换旧类

create constructors for the -init... methods

为-init ...方法创建构造函数

create a destructor for the -dealloc method

为-dealloc方法创建一个析构函数

create other methods which duplicate the functionality

创建其他复制功能的方法

for properties you would probably create getters and setters instead

对于属性,您可能会创建getter和setter

replace the #import with #include directives, as this directive only exists in Objective-C (make sure that the headers you include are protected against multiple includes)

用#include指令替换#import,因为此指令仅存在于Objective-C中(确保包含的头文件不受多个包含的影响)

get rid of usages of NS... classes and methods, as those are part of the Cocoa framework and most probably cannot be ported

摆脱NS ...类和方法的用法,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).

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

#2

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以翻译成C ++,但是在C ++中会有一些没有直接等价的东西。例如:

There is no @encode() compiler directive (which is used for NSValue and a few other classes).

没有@encode()编译器指令(用于NSValue和其他一些类)。

There is no straightforward equivalent to doesNotRecognizeSelector:, respondsToSelector:, conformsToProtocol: or performSelector: (and other methods of similar nature).

没有简单的等效于doesNotRecognizeSelector:,respondsToSelector:,conformsToProtocol:或performSelector :(和其他类似性质的方法)。

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.

在Objective-C中,可以将消息发送到nil,但在C ++中,在空指针上调用成员函数是不行的。

Objective-C allows extending existing classes using class categories, for example, you can add a method to NSString which counts the number of spaces, called numberOfSpaces and it will be available for all NSString instances in your application.

Objective-C允许使用类类别扩展现有类,例如,您可以向NSString添加一个方法,该方法计算空间数,称为numberOfSpaces,它将可用于应用程序中的所有NSString实例。

C++ does not have a finally block for try/catch, but Objective-C has @finally for @try/@catch.

C ++没有try / catch的finally块,但是Objective-C的@finally @ 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.

如果您计划将应用程序发布到多个平台,那么您可以尝试尽可能多地抽象到一个单独的库中。您的iPhone应用程序可以使用Objective-C编写并使用库中的函数,如果您计划将其移植到其框架需要C ++的另一个系统,那么您可以编写C ++应用程序并使用相同库中的相同函数。我想你的库基本上包括[至少]你的绘图例程和核心游戏引擎逻辑。

#1