Should static declarations go in a header file

Question

For public functions I'll put those in a header file such as:

// tree.h
bool TreeIsEmpty(const Tree *ptree);
bool TreeIsFull(const Tree *ptree);
size_t TreeItemCount(const Tree *ptree);

However, what about internal implementation items? Do those only go in my tree.c file or do I also put those into my tree.h file? For example, let's say for TreeItemCount I have a prototype such as:

// tree.c
static bool TreeItemCountInternal(const Tree *ptree);

Do I do anything in the header file with that?

do you mean *declarations* of static functions? (Function definitions contain the function body) — M.M, Mar 15 '21 at 02:20
No, you don't. If they're static, exposing them outside the file that defines them is meaningless at best and error prone at worst — Mad Physicist, Mar 15 '21 at 02:21
@M.M yes sorry I mean putting the declaration in the header file. — carl.hiass, Mar 15 '21 at 02:28

score 2 · Answer 1 · answered Mar 15 '21 at 02:22

2

static bool TreeItemCountInternal(...); has internal linkage, so you wouldn't put anything in the header file.

answered Mar 15 '21 at 02:22

Bill Lynch

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I see. Even so, it's not helpful to show the full declarations of the `c` file in the header? Or is that not the way it works. – carl.hiass Mar 15 '21 at 02:29

Z4-tier · Accepted Answer · 2021-03-15T03:23:48.900

If you were to declare TreeItemCountInternal without designating it as static:

bool TreeItemCountInternal(const Tree *ptree);

then you could put the forward declaration in the header file, and #include that header in you .c files. You might consider doing that if your project spans multiple .c files and you need to share a function across them. The static declaration, when applied to a function, limits it's scope to the translation unit in which it was declared (see this answer for an excellent explanation of what that means from a practical perspective).

Remember that one of the first steps your compiler takes when building a program is to take all of your #include directives, find the file in quesetion, and paste it's contents in place of the #include statement.

There is no dogmatic rule that says you should always put the declaration in the header (although it's often good practice), and the act of doing so-- in and of itself-- does not confer any particular benefit or status (but it could make a lot of difference, depending on how the rest of the program is structured).

Should static declarations go in a header file

2 Answers2