I just have a hard time thinking about some functions that default to internal linkage,are there any? by default of course.

Inline or static functions have internal linkage, non-inline and non-static functions, which I presume you mean by "default" since you don't decorate them with additional keywords, have external linkage.

thanks a lot,that clarifies everything.

Functions (and everything else) in an anonymous namespace have internal linkage as well, since that has deprecated the use of the static qualifier in C++ now.

I know I've responded to you like this before so it kind of feels like I'm picking on you, but... symbols in an anonymous namespace typically have external linkage, they just happen to have a unique name automatically associated with them that is not accessible from the outside.

Wouldn't say it has much of an impact in every-day code, but one place where is matters is for example template parameters: reference of pointer template parameters can only be instantiated with symbols of external linkage. Therefore, you can pass the reference or pointer to a variable within an anonymous namespace, but not a static variable, as a reference or pointer template parameter.

static int bar1 = 0;
namespace { int bar2 = 0; }
 
template<int *> void foo() {}
 
int main() {
    foo<&bar1>(); // error, bar1 does not have external linkage
    foo<&bar2>(); // ok, bar2 has external linkage
}

Not really following you guys.So,if I put a function/variable in a namespace created by me,the function/variable will have internal linkage right?

Unless you make it static, a function or variable in a namespace typically has external linkage. And that applies to anonymous namespaces as well.