[C++] auto

개요

• 타입 추론
• C++11
  • 변수, 람다 파라미터
• C++14
  • 함수 리턴
• C++20
  • 파라미터

예제

• 코드

   #include <cstring>
   #include <iostream>
   #include <string>
      
   using namespace std;
      
   // C++11
   template <typename T> auto func1(T t) -> decltype(t) { return t; }
      
   // C++14
   template <typename T> auto func2(T t) { return t; }
      
   // C++20
   auto func3(auto t) { return t; }
      
   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);
   }
      
   int main() {
   	auto i = 0;
   	auto c = 'a';
   	auto s = "abc";
      
   	cout << type_name<decltype(i)>() << endl;
   	cout << type_name<decltype(c)>() << endl;
   	cout << type_name<decltype(s)>() << endl;
      
   	cout << "------" << endl;
      
   	cout << func1(1) << endl;
   	cout << func2(2) << endl;
   	cout << func3(3) << endl;
      
   	return 0;
   }
  

• 실행 결과

   int
   char
   const char*
   ------
   1
   2
   3