[英]Is there a portable way to know if uintptr_t is defined in stdint.h?
Preamble: I want to convert a pointer to an integer type, eg to check alignment. 前言:我想将指针转换为整数类型,例如检查对齐。 uintptr_t
seems to be the correct type, but it is guaranteed only in C, not in C++ (or C++11) uintptr_t
似乎是正确的类型,但它仅在C中保证,而不是在C ++(或C ++ 11)中保证
For the following code: 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 questions: 2个问题:
I_WONDER_IF_UINTPR_T_IS_DEFINED
? 在放置I_WONDER_IF_UINTPR_T_IS_DEFINED
,我可以使用一个神奇而有保障的单词吗? unsigned long
and forget about it? 我应该只使用unsigned long
而忘记它吗? Generated assembly (when uintptr_t available): http://goo.gl/4feUNK 生成的程序集(当uintptr_t可用时): http : //goo.gl/4feUNK
Note 1: I am aware than in C++11 I should use alignof
in place of sizeof
注1:我知道比在C ++ 11中我应该使用alignof
代替sizeof
Note 2: I am aware of this discussion: <cstdint> vs <stdint.h> 注2:我知道这个讨论: <cstdint> vs <stdint.h>
In general, portable build systems on *nix tend to use the "autotools" approach which is to test-compile a trivial file containing the type in question, and if it compiles, you know you have that type. 通常,* nix上的可移植构建系统倾向于使用“autotools”方法来测试编译包含相关类型的普通文件,如果它编译,你知道你有这种类型。 If you want something simpler, you could either (a) assume uintptr_t
is available even in C++ (probably reasonable), or (b) use unsigned long long
and then: 如果你想要更简单的东西,你可以(a)假设uintptr_t
即使在C ++中也可用(可能是合理的),或者(b)使用unsigned long long
然后:
static_assert(sizeof(unsigned long long) >= sizeof(void*), "oops");
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): 如果你真的想在包含<stdint.h>
的情况下使用不提供uintptr_t
的实现,请考虑使用uintmax_t
,并使用static_assert
以确定是否合适(您已经建立了可能处于愚蠢的设置,因此它可能太小):
#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
There are two dis-advantages though: 但有两个不利因素:
uintmax_t
might not be uintptr_t
, important for overload-resolution and linking. uintmax_t
可能不是uintptr_t
,对于重载解析和链接很重要。 uintmax_t
might be bigger than neccessary. uintmax_t
可能比必要的大。 我知道这是很老了,但是,如何使用UINTPTR_MAX
您I_WONDER_IF_UINTPR_T_IS_DEFINED
?
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