如何检查是否定义了固定宽度的整数 [英] How to check if fixed width integers are defined

问题描述

在 C++ 中，固定宽度的整数被定义为 optional，但我可以'似乎没有找到推荐的方法来检查它们是否被实际定义.

In C++, fixed width integers are defined as optional, but I can't seems to find the recommended way to check if they are actually defined.

检查固定宽度整数是否可用的便携式方法是什么?

What would be a portable way to check if fixed width integers are available?

推荐答案

要确定是否提供了定宽整数类型，可以检查是否有对应的[U]INT*_MAX或 [U]INT*_MIN 宏已定义.

To determine if a fixed-width integer type is provided, you can check if either of the corresponding [U]INT*_MAX or [U]INT*_MIN macros is defined.

// may be necessary for your C++ implementation
#define __STDC_LIMIT_MACROS 
#include <cstdint>

#ifdef INT32_MAX
// int32_t must be available to get here
int32_t some32bitIntVariable;
#endif

根据 7.20 整数类型 ，C11 标准第 4 段(注意加粗部分):

Per 7.20 Integer types <stdint.h>, paragraph 4 of the C11 standard (note the bolded parts):

对于实现提供的此处描述的每种类型， 应声明typedef 名称并定义关联的宏.相反，对于实现未提供的此处描述的每种类型， 不应声明 typedef name 也不应定义关联的宏.

For each type described herein that the implementation provides, <stdint.h> shall declare that typedef name and define the associated macros. Conversely, for each type described herein that the implementation does not provide, <stdint.h> shall not declare that typedef name nor shall it define the associated macros.

C++ 通过 继承了 C 实现.参见 与 ; 一些细节.另请参阅 __STDC_LIMIT_MACROS 的作用 和 __STDC_CONSTANT_MACROS 是什么意思? 有关 __STDC_LIMIT_MACROS 的详细信息.

C++ inherits the C implementation via <cstdint>. See <cstdint> vs <stdint.h> for some details. Also see What do __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS mean? for details on __STDC_LIMIT_MACROS.

因此，如果 int32_t 可用，INT32_MAX 和 INT32_MIN 必须是 #define .相反，如果 int32_t 不可用，则 INT32_MAX 和 INT32_MIN 都不允许被 #define 处理.

Thus, if int32_t is available, INT32_MAX and INT32_MIN must be #define'd. Conversely, if int32_t is not available, neither INT32_MAX nor INT32_MIN are allowed to be #define'd.

请注意，正如@NicolBolas 在另一个答案中所述，可能没有必要实际检查.

Note though, as @NicolBolas stated in another answer, it may not be necessary to actually check.

这篇关于如何检查是否定义了固定宽度的整数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！