This rule is part of MISRA C++:2023.
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prohibited.
Rule 25.5.3 - The pointer returned by the C++ Standard Library functions asctime, ctime, gmtime,
localtime, localeconv, getenv, setlocale or strerror must not be used following a
subsequent call to the same function
Category: Mandatory
Analysis: Undecidable, System
Amplification
Calls to setlocale may change the values accessible through a pointer that was previously returned by localeconv.
For the purposes of this rule:
- A call to
setlocale following a call to localeconv are treated as if they are calls to the same function; and
- Calls to
asctime and ctime are treated as if they are calls to the same function; and
- Calls to
gmtime and localtime are treated as if they are calls to the same function.
Note: calls to setlocale or localeconv within a different thread of execution may lead to violations of
this rule.
Rationale
The C++ Standard Library functions asctime, ctime, gmtime, localtime, localeconv,
getenv, setlocale and strerror return a pointer to an object within the library’s implementation. The
implementation is permitted to use static buffers for any of these objects and a second call (which may occur in a different thread) to the same
function may modify the contents of the buffer. The value accessed through a pointer held by the program before a subsequent call to a function may
therefore change unexpectedly.
Note: the C++ Standard states that the behaviour of the functions covered by this rule is specified in the related version of
ISO 9899 .
Example
void f1()
{
const struct lconv * lc = localeconv();
std::string copy { lc->int_curr_symbol };
const char * res = std::setlocale ( LC_MONETARY, "fr_FR" );
std::cout << lc->int_curr_symbol; // Non-compliant - use after setlocale called
std::cout << copy; // Compliant - copy made before call
std::cout << res; // Compliant - no subsequent call before use
}
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