有没有可移植的方式来知道uintptr_t是否在stdint.h中定义？ [英] Is there a portable way to know if uintptr_t is defined in stdint.h?

问题描述

前置：我想将指针转换为整数类型，例如以检查对准。 uintptr_t 似乎是正确的类型，但仅保证在C中，而不是在C ++（或C ++ 11）

Preamble: I want to convert a pointer to an integer type, e.g. to check alignment. uintptr_t seems to be the correct type, but it is guaranteed only in C, not in C++ (or C++11)

对于以下代码：

#include <stdint.h>
#ifndef I_WONDER_IF_UINTPR_T_IS_DEFINED
  typedef unsigned long uintptr_t;
#endif

template <typename T>
bool isAligned(unsigned char* p) ///Checks alignment with respect to some data type
{
   return !((uintptr_t) p % sizeof(T));
}

template bool isAligned<uint16_t>(unsigned char* p);
template bool isAligned<uint32_t>(unsigned char* p);
template bool isAligned<uint64_t>(unsigned char* p);

2个问题：

• 是否有一个魔法和保证字，我可以使用 I_WONDER_IF_UINTPR_T_IS_DEFINED ？


• 我应该使用<$

生成的程序集（当uintptr_t可用时）： a href =http://goo.gl/4feUNK =nofollow> http://goo.gl/4feUNK

Generated assembly (when uintptr_t available): http://goo.gl/4feUNK

注1 ：我知道比在C + + 11我应该使用 alignof 替换 sizeof

注意2：我知道这个讨论：<cstdint> vs< stdint.h>

Note 1: I am aware than in C++11 I should use alignof in place of sizeof
Note 2: I am aware of this discussion: <cstdint> vs <stdint.h>

推荐答案

如果您真的想使用不提供 uintptr_t 当包括< stdint.h> 时，请考虑使用 uintmax_t ，和 static_assert （您已经建立，您可能会在一个愚蠢的设置，所以它可能太小）：

If you really want to work with an implementation not providing uintptr_t when including <stdint.h>, consider using uintmax_t instead, and a static_assert for suitability (you already established you might be on a goofy setup, so it might be too small):

#include <stdint.h>
static_assert(sizeof(uintmax_t) >= sizeof(void*), "need a bigger unsigned type.");

// Add code using `uintmax_t` to round-trip data-pointers here

虽然有两个缺点：

1. uintmax_t uintptr_t ，对重载解析和连结非常重要。


2. uintmax_t 大于必要。

1. uintmax_t might not be uintptr_t, important for overload-resolution and linking.
2. uintmax_t might be bigger than neccessary.

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