Trigraphs are denoted by a sequence of two question marks followed by a specified third character (e.g. ??- represents a ~ (tilde) character and ??) represents a ] ). They can cause accidental confusion with other uses of two question marks.

Note: the so-called digraphs:

<: :> <% %> %: %:%:

are permitted because they are tokens. Trigraphs are replaced wherever they appear in the program prior to preprocessing.

Example

For example the string

"(Date should be in the form ??-??-??)"

would not behave as expected, actually being interpreted by the compiler as

"(Date should be in the form ~~]"

MISRA-C 2004 Rule 4.2 (required): Trigraphs shall not be used.

Trigraphs are denoted by a sequence of 2 question marks followed by a specified third character (e.g. ??- represents a "~" (tilde) character and ??) represents a "]"). They can cause accidental confusion with other uses of two question marks. For example the string

"(Date should be in the form ??-??-??)"

would not behave as expected, actually being interpreted by the compiler as

"(Date should be in the form ~~]"

MISRA-C++ 2008 Rule 2-3-1 (required): Trigraphs shall not be used.

Rationale

Trigraphs are denoted by a sequence of 2 question marks followed by a specified third character (e.g. ??- represents a "~" (tilde) character and ??) represents a "]"). They can cause accidental confusion with other uses of two question marks.

Example

The string

"(Date should be in the form ??-??-??)"

would probably not meet developer expectations, since the compiler would interpret it as

"(Date should be in the form ~~]"