This rule is part of MISRA C++:2023.
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Rule 25.5.1 - The setlocale and std::locale::global functions shall not be called
[locale] Undefined 9
Category: Required
Analysis: Decidable,Single Translation Unit
Rationale
Calls to setlocale or std::locale::global may introduce data races (leading to undefined behaviour) with
functions that use the locale (e.g. printf, tolower). It is not as easy to guard against these potential data races due to
the ways in which the global locale is used within the C++ Standard Library.
The C++ Standard Library provides functions that allow a locale to be passed as an argument, meaning that it is possible to use a specific locale
without having to depend on the setting of the global locale objects.
Example
void f1()
{
wchar_t c = L'\u2002'; // En-space
std::setlocale( LC_ALL, "ja_JP.utf8" ); // Non-compliant
if ( std::isspace( c ) ) {} // Uses global locale
}
The following example sets the locale without violating this rule:
void f2()
{
wchar_t c = L'\u2002'; // En-space
std::locale utf8( "ja_JP.utf8" );
if ( std::isspace( c, utf8 ) ) {} // Does not use global locale
}
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