A feature of C++ is the ability to create unnamed (anonymous) namespaces, like so:
namespace {
int cannotAccessOutsideThisFile() { ... }
} // namespace
<
Putting methods in an anonymous namespace prevents you from accidentally violating the One Definition Rule, allowing you to never worry about naming your helper methods the same as some other method you may link in.
And, as pointed out by luke, anonymous namespaces are preferred by the standard over static members.