Const function in C

Question

In the source code of git, I saw the following function definition

const char *typename(unsigned int type)
{
    if (type >= ARRAY_SIZE(object_type_strings))
        return NULL;
    return object_type_strings[type];
}

I believed that typename is a function here, but seems be to a const function, which is very confusing to me.

What does this mean and how shall one use this const function feature?

link to source cod; https://github.com/git/git/blob/7d722536dd86b5fbd0c0434bfcea5588132ee6ad/object.c#L29

Answer 1

Use cdecl

% cdecl
cdecl> explain const char *typename(unsigned int)
declare typename as function (unsigned int) returning pointer to const char

It is an useful tool sometimes, but it is quite restricted, for example it said

cdecl> explain const char *typename(unsigned int foo);
syntax error

But it is very useful when trying to make sense of function pointers:

cdecl> declare a as pointer to function (int, double, pointer to const char) 
       returning pointer to const volatile struct foo
const volatile struct foo *(*a)(int , double , const char *)

or

cdecl> explain const void *(*b[])(int , char (*(*)(char ))(double))
declare b as array of pointer to function (int, pointer to function (char) returning pointer
to function (double) returning char) returning pointer to const void