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All occurrences in a source file of the following sequences of three characters (that is, trigraph sequences) are replaced with the corresponding single character.

??=	#		??)	]		??!	|
??(	[		??'	^		??>	}
??/	\		??<	{		??-	~

 

Noncompliant Code Example

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:

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

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size_t i = /* someSome initial value */;
/* assignmentAssignment of i */
if (i > 9000) {
   if (puts("Over 9000!?""?!") == EOF) {
     /* Handle error */
   }
}

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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 MSC00-C. Compile cleanly at high warning levels.)

Automated Detection

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