decltype specifier

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Queries the type of an expression

Contents

[edit] Syntax

decltype ( expression )

[edit] Explanation

decltype is useful when declaring types that are difficult or impossible to declare using standard notation, like lambda-related types or types that depend on template parameters.

[edit] Keywords

decltype

[edit] Example 

#include <iostream>
 
int main() 
{
    int i = 33;
    decltype(i) j = i*2;
 
    std::cout << "i = " << i << ", "
              << "j = " << j << '\n';
 
    auto f = [](int a, int b) -> int {
       return a*b;
    };
 
    decltype(f) f2{f};
    i = f(2, 2);
    j = f2(3, 3);
 
    std::cout << "i = " << i << ", "
              << "j = " << j << '\n';
}

Output: 

i = 33, j = 66
i = 4, j = 9
Retrieved from "http://en.cppreference.com/w/cpp/language/decltype"