Why cPP forward iterators inherit only from input iterators

The

cPP forward iterator needs to implement the interface between the input iterator and the output iterator, but why does it only inherit from the input iterator when implemented?

CPP
Mar.31,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b2bebf-4005e.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b2bebf-4005e.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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