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