Two consecutive question marks signify the start of a trigraph sequence. According to the C99 Standard \ [[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Wiki Markup
All occurrences in a source file of the following sequences of three characters (that is, trigraph sequences) are replaced with the corresponding single character.
??=
#
??)
]
??!
| <ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="d3d3de2a-ef97-4bd8-b6aa-4c2113aafba1"><ac:plain-text-body><![CDATA[
??(
[
??'
^
??>
}
]]></ac:plain-text-body></ac:structured-macro>
??/
\
??<
{
??-
~
Noncompliant Code Example
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