Page History

...

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="815fd5a5abb5e623-120ef15b-4d7f4077-aa348bb2-5543781075e6955137e46d75"><ac:plain-text-body><![CDATA[	??(	[		??'	^		??>	}	]]></ac:plain-text-body></ac:structured-macro>
??/	\		??<	{		??-	~

...

In this noncompliant code example, a++ is not executed because the trigraph sequence ??/ is replaced by \, logically putting a++ on the same line as the comment.

// what is the value of a now??/
a++;

...

The following compliant solution eliminates the accidental introduction of the trigraph by separating the question marks.

// what is the value of a now? ?/
a++;

...

This noncompliant code example includes the trigraph sequence ??!, which is replaced by the character |.

size_t i = /* some initial value */;
if (i > 9000) {
   if (puts("Over 9000!??!") == EOF) {
     /* Handle Error */
   }
}

...

This compliant solution uses string concatenation to concatenate the two question marks; otherwise, they are interpreted as beginning a trigraph sequence.

size_t i = /* some initial value */;
/* assignment of i */
if (i > 9000) {
   if (puts("Over 9000!?""?!") == EOF) {
     /* Handle Error */
   }
}

...