This rule is part of MISRA C++:2023.
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Rule 24.5.1 - The character handling functions from <cctype> and <cwctype> shall not be used
[C11] / 7.4; Undefined 1
[C11] / 7.30.1; Undefined 5
Category: Required
Analysis: Decidable,Single Translation Unit
Amplification
This rule applies to the character classification functions and the character case mapping functions from <cctype> and
<cwctype>.
Note: this rule also applies to the same functions from <ctype.h> and <wctype.h>.
Rationale
The functions declared within <cctype> support the classification and case mapping of characters. Undefined behaviour
occurs if these functions are called with arguments that are not representable as an unsigned char, or that are not equal to the value of
the macro EOF. Similar issues exist for the functions provided by <cwctype>.
The C++ Standard Library provides equivalent classification and case mapping functions within <locale> that are safer to
use.
Note: the C++ Standard states that the behaviour of the functions covered by this rule is defined in the related version of
ISO 9899 .
Example
void f( char c )
{
if ( std::isdigit( c ) ) {} // Non-compliant
if ( std::isdigit( a, std::locale {} ) ) {} // Compliant version of the above
}
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