If you're writing your own malloc(), you could argue you are legitimately part of the system implementation. Those type names are reserved for you.

POSIX is just a bunch of rules some committee made up. People aren't obligated to abide by them. They should get rid of their "reservation" rule, it's pointless since people learn by copying examples and there's tons of _t type examples out there. It's not like the POSIX police will arrest them for it.

C and POSIX are different things though. The only reason why POSIX reserves _t is to avoid potential name collisions, but POSIX moves so slowly that such collisions are rarely a problem (and on any non-UNIX system it's a non-issue anyway).

I *would* have used a prefix for namespacing though, e.g. not `block_t` but `prefix_block_t`.

Essentially everyone does this though...

Ask long as your prefix your types it's unlikely to be a problem

Do you know if any of the popular static analysis tools detect mistakes like this?

Clang has a -Wreserved-identifier warning, but that's only for reserved identifiers in the C standard, not for POSIX (e.g. names starting with double underscore or a single underscore followed by a capital letter).

The C standard has many more such adhoc reserved identifiers, for instance anything starting with `is`, `str` or `wcs` followed by a lowercase letter is technically a reserved identifier, hell, even any preprocessor macro starting with an `E` followed by a digit or uppercase letter is reserved.

Theoretically those reserved identifiers in the C standard matter more than _t because they affect all C code, not just C code targeting POSIX, yet nobody ever brings those up (because these are really only theoretical problems, and should they turn into actual problems one day they are trivial to fix).

It's important to differentiate between the C standard (e.g. what C compilers care about) and the POSIX standard (which C compilers do not care about), since not all C code runs on POSIX systems. It's only on some UNIXes where those two worlds overlap.

In the real-world, using _t typenames really is a complete non-issue.

Also unfortunate are the use of a heap segment representation, and sbrk.

I understand why the use of sbrk is unfortunate but what's wrong with the representation? Are there better ones?