【发布时间】：2010-06-08 02:44:37
【问题描述】：
在 xcode 中，在使用 gcc 编译应用程序时，如果 NSZombieEnabled 之类的功能在分发版本中打开，我想抛出编译时错误，从而确保编译将失败并且我不会意外地做一些愚蠢的事情。
我做了一些谷歌搜索，但无法弄清楚如果满足某个条件，如何使编译器退出。肯定很简单吧，我是不是没找到？
【问题讨论】：
标签： iphone objective-c xcode gcc compiler-construction
【发布时间】：2010-06-08 02:44:37
【问题描述】：
#if SHOULD_FAIL
#error "bad compiler!"
#endif
int main()
{
return 0;
}
由于NSZombieEnabled 是一个环境变量，您需要在构建脚本中做一些巧妙的事情来将您的宏定义为零或一。
严格来说，#error 指令出现在 C 预处理器中，而不是 gcc。但在你描述的情况下，这应该无关紧要。
【讨论】：
-
这似乎很难……似乎找不到方法
-
@coneybeare：NSZombieEnabled 是您在运行时设置的环境变量。您无需在编译时担心它。但是，如果您有编译时调试宏，则此技术很有用。
-
+1 请注意，您也可以通过
#warning This is a warning发出警告而不是错误。
NSZombieEnabled 是一个环境标志，据我所知，它不会影响生成的二进制文件（尽管它可能会影响编译速度。）
【讨论】：
一个编译时断言()--a.k.a.静态断言——可能会有所帮助。这是我的，主要来自http://www.pixelbeat.org/programming/gcc/static_assert.html：
/*-----------------------------------------------------------------------------
* Compile-time ASSERT(). Similar to the BOOST_STATIC_ASSERT(). And the C++0x
* static_assert(), which also has a parameter for a useless error message
* (see correction!). Our ASSERT() can be placed anywhere in the code, except:
*
* o In a twice-included header file, without a #ifndef...#endif wrapper.
* o In the middle of a structure definition (or enum definition).
* o In C89 or C90, after a statement. But you can wrap it in braces!
*
* If you want stick something in the middle of a structure definition
* you'll need to use the ugly, three-line construct #if...#error...#endif.
* And if you do do this, the pre-processor has a much more limited idea of
* what a "constant expression" is.
*
* This is a refinement of ideas from the web (www.pixebeat.org is good). It
* is shorter than BOOST. And, I believe, is better than Linus Torvald's
* suggestion for an improved BUILD_BUG_ON(). And the do{...}while(0) wrapper
* you commonly see is totally inapplicable here: it limits permissible
* locations.
*
* The web has many suggestions using arrays with a negative index. But with
* GCC, most of these do not detect a NON-CONSTANT arg (which is easy enough
* to do in error), except for the attractive 'extern int foo[expression]',
* which also gives an 'unused variable' warning (which might be fixable via
* (void)foo). GCC 4.3 apparently has a built-in static_assert(). Update:
* typedef int array[expression] seems also to be good.
*/
#define CONCAT_TOKENS(a, b) a ## b
#define EXPAND_THEN_CONCAT(a,b) CONCAT_TOKENS(a, b)
#define ASSERT(e) enum {EXPAND_THEN_CONCAT(ASSERT_line_,__LINE__) = 1/!!(e)}
但我更正了我对 C++0x 中“无用”消息的看法：
/*-----------------------------------------------------------------------------
* Correction!: The message in static_assert() isn't quite useless, and we've
* added it to ASSERTM(). This is needed for the case where two different
* header files happen by chance to have two ASSERT()'s on the same line, or
* likewise for a source file and a header file.
*
* We could also handle this via __COUNTER__, but this isn't supported by
* the SGI compiler (and is uglier). And we can't use __FILE__, because it
* doesn't usually expand to a valid C token (e.g. it has a dot c or dot h).
*/
#define ASSERTM(e,m) enum{EXPAND_THEN_CONCAT(m##_ASSERT_line_,__LINE__)=1/!!(e)}
一些例子：
/*-----------------------------------------------------------------------------
* Example:
*/
ASSERTM (sizeof (int16) == 2, my_global_header_h);
ASSERTM (sizeof (ord32) == 4, my_global_header_h);
ASSERTM (sizeof (int64) == 8, my_global_header_h);
/*-----------------------------------------------------------------------------
* Equally good, I believe, is the following variant, but it is slightly
* longer (and not used by us at the present time):
*/
#define ASSERTt(e) typedef int EXPAND_THEN_CONCAT(ASSERT_line_,__LINE__)[1-2*!(e)]
【讨论】：
您可以做的另一件有趣的事情是操纵构建脚本的输出。如果您在构建过程中使用自定义构建脚本，则可以执行以下操作：
echo "error: this build step failed!"
或者：
echo "warning: this build step could be potentially faulty"
这些将产生错误或警告（分别）将显示在构建结果窗口中。我已经用过几次了，它真的很有用。
【讨论】：