外部变量声明没有内部链接

Question

I'm asking this question as a follow up from this post. They say that the extern block declaration has external linkage and not internal linkage, but I'm not sure why:

static int i = 0; // #1
void g() {
    extern int i; // #3 external linkage
}

Why doesn't the extern declaration take the linkage of i (internal linkage)? The quote in the post seems to allow that. In the example after the OP's quote it has:

static void f();
void g() {
    extern void f(); // internal linkage
    // ...
}

and it says that the extern declaration has internal linkage. Why is there a difference when using variables and functions?

Answer 1

Because variable "i" has static storage. So, in terms of your snippet,

• omitting the "static" statement will produce "no linkage"
• applying "static" statement will produce "external linkage" (as static storage is quite special part of the C/C++ runtime infrastructure).

Also, you may find this discussion interesting: Understanding static storage class in C