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Asked: 2026-05-16T06:08:25+00:00

I recently came upon the need to have compile-time assertions in C++ to check

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I recently came upon the need to have compile-time assertions in C++ to check that the sizes of two types were equal.

I found the following macro on the web (stated to have come from the Linux kernel):

#define X_ASSERT(condition) ((void)sizeof(char[1 - 2*!!(condition)]))

which I used like so:

X_ASSERT(sizeof(Botan::byte) != sizeof(char));

This gets me curious – although this works, is there a cleaner way to do so? (obviously there’s more than one way, as it is) Are there advantages or disadvantages to certain methods?

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  1. Editorial Team

    You might want to take a look at Boost StaticAssert. The internals aren’t exactly clean (or weren’t the last time I looked) but at least it’s much more recognizable, so most people know what it means. It also goes to some pains to produce more meaningful error messages if memory serves.

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