9608f67c32
- Add an example with a local locale - Add links to documentation - Correct a few typos - I did not add an independent example using the global locale but added a comment
104 lines
3.3 KiB
Plaintext
104 lines
3.3 KiB
Plaintext
== Why is this an issue?
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The ``++chrono++`` library, introduced in {cpp}20, provides support for calendars, time zones, and i/o formatting and parsing operations on time-related objects.
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``++chrono++`` is a better alternative to the C/POSIX functions that operate on ``++time_t++``, ``++tm++``, or ``++timespec++`` types. In comparison to C facilities, it provides better integration with other components of the {cpp} standard library (``++iostreams++`` and ``++format++``). Also, it supports compile-time computation and it is thread-safe.
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This rule raises an issue C/POSIX functions that can be replaced with one of the ``++std::chrono++`` components:
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* querying for current time (``++time++``, ``++timespec_get++``, ``++clock_gettime++``)
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* date to time-point conversion (``++mktime++``, ``++gmtime++``, ``++localtime++``)
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* time serialization (``++ctime++``, ``++asctime++``, ``++strftime++``)
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* time parsing (``++strptime++``)
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=== Noncompliant code example
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[source,cpp]
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----
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int currentMonth() {
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std::time_t tp;
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std::time(&tp);
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std::tm* date = std::gmtime(&tp);
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return date->tm_mon + 1;
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}
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std::chrono::system_clock::time_point makeSomeDay() {
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// Creates time_point corresponding to 2020-09-04
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std::tm date{};
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date.tm_year = 120;
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date.tm_mon = 8;
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date.tm_mday = 4;
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std::time_t t = std::mktime(&date); // Noncompliant
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return std::chrono::system_clock::from_time_t(t);
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}
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std::optional<int> yearOfTimePoint(std::chrono::system_clock::time_point tp) {
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std::time_t t = std::chrono::system_clock::to_time_t(tp);
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std::tm* date = std::gmtime(&t); // Noncompliant
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if (!date)
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return std::nullopt;
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return date->tm_year + 1900;
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}
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std::string toString(std::chrono::system_clock::time_point tp) {
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std::time_t t = std::chrono::system_clock::to_time_t(tp);
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std::tm* date = std::gmtime(&t); // Noncompliant
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if (!date)
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throw InvalidDate();
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std::string buffer(100, ' ');
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std::size_t written = std::strftime(&buffer[0], buffer.size(), "%A %c", date);
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buffer.resize(written);
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return buffer;
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}
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std::string toFrenchString(std::chrono::system_clock::time_point tp) {
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auto oldLocale = std::locale::global(std::locale("fr_FR.UTF-8"));
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std::string result = toString(tp);
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std::locale::global(oldLocale);
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return result;
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}
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----
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=== Compliant solution
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[source,cpp]
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----
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std::chrono::month currentMonth() {
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using namespace std::chrono;
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auto dp = floor<days>(system_clock::now());
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return year_month_day(dp).month();
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}
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std::chrono::system_clock::time_point makeSomeDay() {
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using namespace std::chrono;
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return sys_days(2020y/September/4);
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}
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std::optional<std::chrono::year> yearOfTimePoint(std::chrono::system_clock::time_point tp) {
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using namespace std::chrono;
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year_month_day date(floor<days>(tp));
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if (!date.ok())
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return std::nullopt;
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return date.year();
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}
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std::string toString(std::chrono::system_clock::time_point tp) {
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return std::format("{:%A %c}", tp); // Or "{:L%A %c}" if you want to use the global locale
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}
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std::string toFrenchString(std::chrono::system_clock::time_point tp) {
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return std::format(std::locale("fr_FR.UTF-8"), "{:L%A %c}", tp);
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}
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----
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== Resources
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=== Documentation
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* {cpp} reference - https://en.cppreference.com/w/cpp/chrono[Date and time utilities]
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* {cpp} reference - https://en.cppreference.com/w/cpp/chrono/system_clock/formatter#Format_specification[Formatting `std::chrono::sys_time`]
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