Is t_whatever a reserved name in the C standard or POSIX?

Question

As far as I know:

an underscore (‘_’) and all identifiers regardless of use that begin with either two underscores or an underscore followed by a capital letter are reserved names

In Posix: Names that end with ‘_t’ are reserved for additional type names.

In addition: The header file sys/stat.h reserves names prefixed with ‘st_’ and ‘S_’.

Can we use "t_whatever" (e.g. t_node) to define our own types?

Answer 1

Yes, you can certainly use t_ as a prefix, that's not in any reserved space.

Personally I wouldn't recommend doing so, but that's mainly because I'm not convinced that having a prefix to make a type name more obviously a type name is a win, in very many cases.

I can't see that

t_node head;

is better than

node head;

In fact, I think the latter is more readable. It's very often the case that you see from usage immediately if a word is a type or variable name in C, in my opinion.

One objection might be that it can be unclear when using sizeof, for instance consider dynamically allocating a new node. Many people would write that as:

t_node *head = malloc(sizeof(t_node));

but I'm very set against that usage; I consider it better to avoid handing type names to sizeof whenever possible, and use the variable instead, thus "locking" the size to the destination type which is a good thing:

node *head = malloc(sizeof *head);

Also, as usual, note that I would never write the first example exactly like that, since I think it makes sizeof look like a function. I always have a space:

t_node *head = malloc(sizeof (t_node));