Two consecutive question marks signify the start of a trigraph sequence. According to the C standard [ISO/IEC 9899:2011],
All occurrences in a source file of the following sequences of three characters (that is, trigraph sequences) are replaced with the corresponding single character.
??=
#
??)
]
??!
|
??(
[
??'
^
??>
}
??/
\
??<
{
??-
~
...
| Code Block | ||||
|---|---|---|---|---|
| ||||
size_t i = /* some initial value */;
/* assignment of i */
if (i > 9000) {
if (puts("Over 9000!?""?!") == EOF) {
/* Handle Error */
}
}
|
The above code This code prints Over 9000!??!, as intended.
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CERT C++ Secure Coding Standard: PRE07-CPP. Avoid using repeated question marks
ISO/IEC 9899:2011 Section Section 5.2.1.1, "Trigraph sequences"
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