UL后缀vs uint32_t转换 [英] UL suffix vs uint32_t cast

问题描述

我必须这样定义常量:

#define MY_CONSTANT   0xBEEF

我想确保我的常量将被视为32位.

I want to be sure that my constant will be considered 32 bits.

我可以像这样使用(uint32_t)转换:

I have can use a (uint32_t) cast like this :

#define MY_CONSTANT   (uint32_t)0xBEEF

或者像这样的UL后缀:

Or a UL suffix like this :

#define MY_CONSTANT   0xBEEFUL

这两个版本完全相同吗?

Are these two versions fully equivalent?

我会说不，因为UL等同于 unsigned long 和 unsigned long 长度可能取决于CPU.

I would say no, as UL is the equivalent of unsigned long and unsigned long length may depend on CPU.

C99标准确保 uint32_t 整数为32位，但是我不认为这可以确保 UL 后缀具有相同的功能.

The C99 standard ensures that an uint32_t integer is 32 bits, but I don't think it ensures that a UL suffix does the same.

推荐答案

您是对的，由于您提到的原因，它们并不相同.不能保证 uint32_t 是 unsigned long 的别名.如有必要，在 #define 中包含演员表.

You're right, they're not equivalent for the reason you mention. There's no guarantee that uint32_t is an alias for unsigned long. Include the cast in the #defines if necessary.

您应该使用括号，请参阅@Keith Thompson的评论，这是有充分理由的；否则 sizeof 将不起作用.

You should use the parentheses, see comment by @Keith Thompson for a very good reason why; otherwise sizeof won't work.

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