问题
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.
回答1:
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.
回答2:
Based on Sparky's answer, here is a way that would look a bit nicer (by eliminating the explicit numbers)
#include <limits.h>
#include <stdint.h>
//Check if size if 4bytes
#if UINT_MAX == UINT32_MAX
....
#endif
<limits.h> defines INT_MAX and <stdint.h> defines UINT32_MAX. Generally, <stdint.h> gives integer types with specified widths.
来源：https://stackoverflow.com/questions/2584937/checking-the-sizeof-an-integer-type-in-the-preprocessor