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Two consecutive question marks signify the start of a trigraph sequence. According to the C99 Standard \[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\]: |
All occurrences in a source file of the following sequences of three characters (that is, trigraph sequences) are replaced with the corresponding single character.
??=
#
??)
]
??!
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[
??'
^
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}
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\
??<
{
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~
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Inadvertent trigraphs can result in unexpected behavior. Some compilers provide options to warn when trigraphs are encountered or to disable trigraph expansion. Use the warning options and ensure your code compiles cleanly. (see See guideline MSC00-C. Compile cleanly at high warning levels.).
Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
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PRE07-C | low | unlikely | medium | P2 | L3 |
Automated Detection
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Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Other Languages
This rule appears in the C++ Secure Coding Standard as : PRE07-CPP. Avoid using repeated question marks.
Bibliography
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\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 5.2.1.1, "Trigraph sequences" \[[MISRA 042004|AA. Bibliography#MISRA 04]\] Rule 4.2 |
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