检查预处理器中整数类型的大小
如何在 g++ 下的预处理器中检查 unsigned 的大小？ sizeof 是不可能的，因为它在预处理期间没有定义。
How can I check the size of an unsigned in the preprocessor under g++? sizeof is out of the question since it is not defined when during preprocessing.
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这可能不是最优雅的方法，但您可以利用的一件事是“limits.h”中定义的 UINT_MAX。也就是说，...
如果 UINT_MAX == 65535，那么您会知道 sizeof (unsigned) = 2
如果 UINT_MAX == 4294967295，那么您会知道 sizeof (unsigned) = 4。
依此类推。
正如我所说，它并不优雅，但它应该提供一定程度的可用性。
希望这有帮助。
This may not be the most elegant method, but one thing that you may be able to leverage is UINT_MAX defined in "limits.h". That is, ...
if UINT_MAX == 65535, then you would know that sizeof (unsigned) = 2
if UINT_MAX == 4294967295, then you would know that sizeof (unsigned) = 4.
and so on.
As I said, not elegant, but it should provide some level of usability.
Hope this helps.
根据 Sparky 的回答，这里有一种看起来更好的方法（通过消除显式数字）
INT_MAX和< stdint.h>定义UINT32_MAX。一般来说，Based on Sparky's answer, here is a way that would look a bit nicer (by eliminating the explicit numbers)
<limits.h>definesINT_MAXand<stdint.h>definesUINT32_MAX. Generally,<stdint.h>gives integer types with specified widths.如果要检查表达式
sizeof(unsigned)的值与某个数字是否相等，可以使用按位左移 (<<) 。此操作仅适用于
unsigned类型。如果你想检查条件
sizeof(unsigned) <= 32，那么检查条件1 <<; 就足够了。 32==0。因此，要测试条件
sizeof(unsigned) > 31，需要测试1 << 31！= 0。因此，要测试条件
sizeof(unsigned) == 32，您可以使用以下命令：If you want to check the value of the expression
sizeof(unsigned)on the equality with a certain number, you can use bitwise shift to the left (<<).This operation just works with type
unsigned.If you want to check condition
sizeof(unsigned) <= 32, then it is enough to check the condition1 << 32 == 0.Accordingly, to test the condition
sizeof(unsigned) > 31, you need to test1 << 31 != 0.As a result, to test the conditions
sizeof(unsigned) == 32you can use this: