是“NSString * __unused aString”和“NSString__unused * aString”当量？ [英] Are "NSString * __unused aString" and "NSString __unused * aString" equivalent?

问题描述

1. 是 NSString * __unused aString 和 NSString __unused * aString




2. - （void）aMethod：（NSString * __unused）aString

   b

3. 如果答案是是，我应该选择哪种形式是正确的？

<当启用/停用 GCC_WARN_UNUSED_PARAMETER 和 GCC_WARN_UNUSED_VARIABLE 指令时，这两种格式的两种格式似乎都一样。

我没有找到任何信息来澄清这一点。

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相关主题： / p>

__ unused Flag行为/用法（具有目标C的GCC）

解决方案

两者之间有区别。

当属性 __未使用出现在星号之前时，它会装饰整个声明列表的主类型。所有变量将未使用：


__unused NSString * foo，* bar; // 好。所有变量在语句中未使用。
NSString __unused * foo，* bar; // OK


但是放在 * 后面将仅适用于第一个变量：


NSString * __unused foo，* bar; //未使用的变量'bar'


我更喜欢 NSString * __unused foo; 因为它看起来更清楚我不会隐藏罕见的情况下，当我在一个语句中声明多个变量。

GCC属性语法参考在第6.31节中提到它：

一个属性说明符列表可能会出现在声明器
（不是第一个）之前，用逗号分隔的声明器列表中的
声明多个标识符使用单个列表
说明符和限定符。这种属性说明符仅适用于出现其声明符之前的
标识符。例如，在

  __attribute __（（noreturn））void d0（void），
 __attribute __ ，1,2）））d1（const char *，...），
 d2（void）
  

noreturn属性应用于所有声明的函数; format属性只适用于d1。

1. Are NSString * __unused aString and NSString __unused * aString equivalent, when they are variable declarations?

2. Are - (void)aMethod:(NSString * __unused)aString and - (void)aMethod:(NSString __unused *)aString equivalent, when they are Objective-C method parameter declarations?

3. If the answer is "yes", what form should I prefer as correct?

Both forms in both cases seem to work identically when enabling/disabling GCC_WARN_UNUSED_PARAMETER and GCC_WARN_UNUSED_VARIABLE directives.

I didn't find any information to clarify this.

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Relevant topics:

__unused Flag Behavior/Usage (GCC with Objective C)

解决方案

There is a difference between the two.

When the attribute, __unused, appears before the star, it decorates the primary type of the entire declaration list. All variables will be "unused":

__unused NSString *foo, *bar; // OK. All variables are unused in the statement. NSString __unused *foo, *bar; // OK

But when placed after the *, it will only apply to the first variable:

NSString * __unused foo, *bar; // Unused variable 'bar'

I prefer NSString * __unused foo; because it seems more clear to me and won't hide the rare case when I declare multiple variables in one statement.

The GCC Attribute Syntax reference mentions it in Section 6.31:

An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers. Such attribute specifiers apply only to the identifier before whose declarator they appear. For example, in

 __attribute__((noreturn)) void d0 (void),
     __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
      d2 (void) 

the noreturn attribute applies to all the functions declared; the format attribute only applies to d1.

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