Question

I noticed a very curious behavior that, if standard, I would be very happy to exploit (what I’d like to do with it is fairly complex to explain and irrelevant to the question).

The behavior is:

static void name();
void name() {
    /* This function is now static, even if in the declaration
     * there is no static keyword. Tested on GCC and VS. */
}

What’s curious is that the inverse produces a compile time error:

void name();
static void name() {
    /* Illegal */
}

So, is this standard and can I expect other compilers to behave the same way? Thanks!

Answer 1

C++ standard:

7.1.1/6: “A name declared in a namespace scope without a
storage-class-specifier has external
linkage unless it has internal linkage
because of a previous declaration” [or unless it’s const].

In your first case, name is declared in a namespace scope (specifically, the global namespace). The first declaration therefore alters the linkage of the second declaration.

The inverse is banned because:

7.1.1/7: “The linkages implied by successive declarations for a given
entity shall agree”.

So, in your second example, the first declaration has external linkage (by 7.1.1/6), and the second has internal linkage (explicitly), and these do not agree.

You also ask about C, and I imagine it’s the same sort of thing. But I have the C++ book right here, whereas you’re as capable of looking in a draft C standard online as I am 😉