Discussing the constness implied by various const keyword placements.

[ Check out all posts in “c-cpp” series here. ]

It is known that declaration grammar in C/C++ can get pretty cryptic. But for reasons unknown to me, it is made even worse by introducing inconsistencies to the rules.

The position of the const keyword is what I am thinking of. There is actually a pretty consistent way to declare things constant: It can be placed on the right of the thing that it qualifies as const.

int const x;

More complex:

int const * const xp;
\_______/ \_____/

But C/C++ allows you to place that leftmost const on the other side.

const int * const xp;
\_______/ \_____/

And unfortunately, that’s the popular (or even canonical, considering it being used in most texts) style. So I guess every newcomer starts by first learning the exception that doesn’t scale to more elaborate declarations, only to then relearn how to read things later.

Here is a good SO discussion about the general rule: What is the difference between const int*, const int * const, and int const *?. It links to a few other useful pages as well.

Thanks for reading! If you find technical errors, please report in the blog’s Issues page.