我如何知道编译器是否启用了ARC支持？ [英] How do I know whether the compiler has ARC support enabled?

问题描述

我需要在我的iOS应用程序中编写一个lib。

I need to write a lib in my iOS app.

该语句应该预处理定义为：

The statement should be pre-process define as :

myObject ...

#if ARC
   // do nothing
#else
   [myObject release]
#endif

或运行时流程：

if (ARC) {
   // do nothing
} else {
   [myObject release];
}

我该怎么办？

请帮帮我！谢谢。

推荐答案

您可以使用 __ has_feature ，如下所示：

You can use __has_feature, like so:

#if __has_feature(objc_arc)
// ARC is On
#else
// ARC is Off
#endif

如果你想用GCC构建（Apple的GCC确实如此）不支持ARC），您可能还需要以下内容来确定编译器：

If you want to also build with GCC (Apple's GCC does not support ARC), you may also need the following to determine the compiler:

#if defined(__clang)
// It's Clang
#else
// It's GCC
#endif

更新

综合起来，它们会采用一般形式：

Combined, they would take the general form:

 #if defined(__clang)     

 #if !defined(__has_feature)
 // idk when clang introduced this
 #error This version of clang does not support __has_feature
 #endif

 #define MON_IS_ARC_ENABLED_IN_THIS_TRANSLATION __has_feature(objc_arc)

 #else
 // for every compiler other than clang:

 #if defined(__has_feature)
 #error Another compiler supports __has_feature
 #endif

 #define MON_IS_ARC_ENABLED_IN_THIS_TRANSLATION 0

 #endif

然后在您的来源中使用 MON_IS_ARC_ENABLED_IN_THIS_TRANSLATION 或进一步 #define s。

Then just use MON_IS_ARC_ENABLED_IN_THIS_TRANSLATION in your sources or for further #defines.

如果您使用的编译器添加支持，则必须为此添加一个案例（并且编译器错误可能会捕获在这种情况下的错误，因为它可能禁止使用ref count ops）。

If a compiler you use adds support, you would have to add a case for that (and compiler errors would likely catch the error in this case, since it would likely forbid use of ref count ops).

请注意，这有额外的检查来证明人们如何（也应该）避免定义保留标识符（基于评论中的对话）。它并非详尽无遗，而是一场演示。如果您发现自己经常编写条件 __ has_feature 检查，则可能需要为此定义一个新宏来减少和简化定义。

Note that this has extra checks to demonstrate how one can (and should) avoid defining reserved identifiers (based on a conversation in the comments). It's not exhaustive, but a demonstration. If you find yourself writing conditional __has_feature checks often, you may want to define a new macro for that to reduce and simplify definitions.

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