code>; and both <code>E</code> itself and <code>E.message()</code> are reasonable to print/log/analyze in that event. There is a wide range of Flow-IPC error codes indicating what went wrong; system (<code>errno</code>-based) and Boost codes may be generated too. Reference documentation announces which codes are possible for which APIs.</li>
<li>If it is not null: On success, the <code>Error_code</code> pointee is cleared (made falsy). On error it is filled with a truthy code <code>E</code>. See preceding p