title: What does this External Linkage directive mean?
body: <p>Can someone explain this note in <em>C++ primer 5th edition</em> to me:</p>
  <blockquote>
  <p>Note</p>
  <p>The functions that C++ inherits from the C library are permitted to be defined as C functions but are not required to be C functions—it’s up to each C++ implementation to decide whether to implement the C library functions in C or C++.</p>
  </blockquote>