TIOBE - C Coding Standard

Guideline: 12.1#2

This rule is Obsolete
Synopsis:	Avoid writing two adjacent question marks anywhere within your source code.
Language:	C
Severity Level:	6
Category:	PREPROCESSING

Description:

Avoiding adjacent question marks eliminates any possible confusion with trigraphs. Note in particular the, once common, practice of using ? as a place holder in a string is very dangerous.

Example:

char date[20] = "??-??-??";
/* This is actually replaced with: */
char date[20] = "~~??";