如何检查__builtin_函数在gcc上可用 [英] How to check __builtin_ function is available on gcc

问题描述

我需要知道gcc是否有一种方法可以检查那些很棒的 __ builtin_MY_DESIRED_FUNCTIONs

I need to know is there a method for gcc to check presence of those awesome __builtin_MY_DESIRED_FUNCTIONs

例如，我想使用 __ builtin_nan 并确保它可用于我的程序，并且在编译期间不会失败.

For example, I'd like to use __builtin_nan and be sure it is available for my program and it won't fail during compilation time.

我会更具体:在clang上有 __ has_builtin "checker"，这样我们就可以像

I'll be more specific: on clang there is __has_builtin "checker" so we can write smth like

#if __has_builtin(__builtin_nan)

但是我找不到gcc的类似物.

But I can't find analog for gcc.

也许我可以仅仅依靠gcc，例如哦，我现在在gcc上，让我们假设所有这些 __ builtin _ 都在下面的示例中……"

And probably I can rely just on gcc, like "Oh, I'm on gcc now, just let's assume all of those __builtin_ are here like in example below..."

#if __GNUC__
double mynan = __builtin_nan("0");
#endif

在有人放置此"-fno-builtin"编译标志之前，它可能会起作用.

And probably it will work, till someone put this "-fno-builtin" compilation flag.

推荐答案

否，您将不得不使用 __ GNUC __ 和 __ GNUC_MINOR __ (和 __ GNUC_PATCHLEVEL __ >如果您使用的是此类gcc版本)，请测试每个版本特定的内置功能(可以在此处)

No, you will have to use __GNUC__ and __GNUC_MINOR__ (and __GNUC_PATCHLEVEL__ if you use such gcc versions) to test for each release specific builtin function (gcc releases can be found here)

例如:

/* __builtin_mul_overflow_p added in gcc 7.4 */
#if (__GNUC__ > 7) || \
         ((__GNUC__ == 7) && (__GNUC_MINOR__ > 3))
#define BUILTIN_MUL_OVERFLOW_EXIST
#endif

#ifdef BUILTIN_MUL_OVERFLOW_EXIST
int c = __builtin_mul_overflow_p (3, 2, 3) ? 0 : 3 * 2;
#endif

此处有一个完全符合您要求的公开错误..

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