[C++] literals

개요

• 표준 리터럴

  • 종류	접미사	의미	버전
    string_literals	s	string	C++14
    string_view_literals	sv	string_view	C++17
    complex_literals	i	complex	C++14
    	if	complex	C++14
    	il	complex	C++14
    chrono_literals	y	chrono::year	C++20
    	d	chrono::day	C++20
    	h	chrono::hours	C++14
    		chrono::duration<long int, std::ratio<3600> >	C++14
    	min	chrono::minutes	C++14
    		chrono::duration<long int, std::ratio<60> >	C++14
    	s	chrono::seconds	C++14
    		chrono::duration	C++14
    	ms	chrono::milliseconds	C++14
    		chrono::duration<long int, std::ratio<1, 1000> >	C++14
    	us	chrono::microseconds	C++14
    		chrono::duration<long int, std::ratio<1, 1000000> >	C++14
    	ns	chrono::nanoseconds	C++14
    		chrono::duration<long int, std::ratio<1, 1000000000> >	C++14

• 사용자 정의 리터럴
  • _를 이용
  • 사용 가능한 파라미터

    • 파라미터	버전
      const char *	C++11
      unsigned long long int	C++11
      long double	C++11
      char	C++11
      wchar_t	C++11
      char8_t	C++20
      char16_t	C++11
      char32_t	C++11
      const char * , std::size_t	C++11
      const wchar_t * , std::size_t	C++11
      const char8_t * , std::size_t	C++20
      const char16_t * , std::size_t	C++11
      const char32_t * , std::size_t	C++11

예제

• 코드

   #include <chrono>
   #include <complex>
   #include <cstring>
   #include <iostream>
   #include <string>
      
   using namespace std;
      
   class Test {
   	public:
   		Test(int i) { cout << "Test(int i)" << endl; }
   		Test(string s) { cout << "Test(string s)" << endl; }
      
   		void func(){};
   };
      
   Test operator""_t(unsigned long long int l) {
   	return Test(static_cast<int>(l));
   }
      
   Test operator""_t(const char *c, size_t t) {
   	cout << t << endl;
   	return Test(c);
   }
      
   template <typename T> constexpr string type_name() {
   	const string s = __PRETTY_FUNCTION__;
   	const int prefixSize = s.find("[with T = ") + strlen("[with T = ");
      
   	return string(s.data() + prefixSize, s.find(';') - prefixSize);
   }
      
   void user_defined_literals_test() {
   	Test t1 = 1_t;
   	t1.func();
      
   	Test t2 = "abc"_t;
   	t2.func();
   }
      
   void string_literals_test() {
   	using namespace string_literals;
      
   	cout << type_name<decltype("a")>() << endl;
   	cout << type_name<decltype("a"s)>() << endl;
   }
      
   void string_view_literals_test() {
   	using namespace string_view_literals;
      
   	cout << type_name<decltype("a"sv)>() << endl;
   }
      
   void complex_literals_test() {
   	using namespace complex_literals;
      
   	cout << type_name<decltype(1.1i)>() << endl;
   	cout << type_name<decltype(1.1if)>() << endl;
   	cout << type_name<decltype(1.1il)>() << endl;
   }
      
   void chrono_literals_test() {
   	using namespace chrono_literals;
      
   	cout << type_name<decltype(1y)>() << endl;
   	cout << type_name<decltype(1d)>() << endl;
   	cout << type_name<decltype(1h)>() << endl;
   	cout << type_name<decltype(1min)>() << endl;
   	cout << type_name<decltype(1s)>() << endl;
   	cout << type_name<decltype(1ms)>() << endl;
   	cout << type_name<decltype(1us)>() << endl;
   	cout << type_name<decltype(1ns)>() << endl;
   }
      
   int main() {
   	user_defined_literals_test();
      
   	cout << "------ 1" << endl;
      
   	string_literals_test();
      
   	cout << "------ 2" << endl;
      
   	string_view_literals_test();
      
   	cout << "------ 3" << endl;
      
   	complex_literals_test();
      
   	cout << "------ 4" << endl;
      
   	chrono_literals_test();
      
   	return 0;
   }
  

• 실행 결과

   Test(int i)
   3
   Test(string s)
   ------ 1
   const char (&)[2]
   std::__cxx11::basic_string<char>
   ------ 2
   std::basic_string_view<char>
   ------ 3
   std::complex<double>
   std::complex<float>
   std::complex<long double>
   ------ 4
   std::chrono::year
   std::chrono::day
   std::chrono::duration<long int, std::ratio<3600> >
   std::chrono::duration<long int, std::ratio<60> >
   std::chrono::duration<long int>
   std::chrono::duration<long int, std::ratio<1, 1000> >
   std::chrono::duration<long int, std::ratio<1, 1000000> >
   std::chrono::duration<long int, std::ratio<1, 1000000000> >