Checking the sizeof an integer type in the preproc

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.