std::is_trivially_constructible in C++ with Examples

The std::is_trivially_constructible template of C++ STL is present in the <type_traits> header file. The std::is_trivially_constructible template of C++ STL is used to check whether the given type T is trivially constructible type with the set of arguments or not. It return the boolean value true if T is trivially constructible type, otherwise return false.

Header File:

#include<type_traits>

Template Class:

template <class T, class.. Args>
struct is_trivially_constructible;

Syntax:

std::is_trivially_constructible::value

Parameters: The template std::is_trivially_constructible accepts two parameter:

• T: A data type, or an array of unknown bound.
• Args: A list of data types representing the argument types for the constructor form, in the same order as in the constructor.

Return Value: This template returns a boolean variable as shown below:

• True: If the type T is a trivially constructible type.
• False: If the type T is not a trivially constructible type.

Below is the program to illustrates the std::is_trivially_constructible template in C/C++:

Program 1:

// C++ program to illustrate
// std::is_trivially_constructible
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

// Declare structures
struct Ex1 {
    std::string str;
};
struct Ex2 {
    int n;
    Ex2() = default;
};

struct A {

    // Constructor
    A(int, int){};
};

// Driver Code
int main()
{
    cout << boolalpha;

    // Check if Ex1 is a trivally
    // constructible or not
    cout << "Ex1: "
         << is_trivially_constructible<Ex1>::value
         << endl;

    // Check if struct Ex2 is a trivally
    // constructible or not
    cout << "Ex2: "
         << is_trivially_constructible<Ex2>::value
         << endl;

    // Check if A(int, float) is a trivally
    // constructible or not
    cout << "A(int, int): "
         << is_trivially_constructible<A(int, int)>::value
         << endl;
    return 0;
}

Output:

Ex1: false
Ex2: true
A(int, int): false

Program 2:

// C++ program to illustrate
// std::is_trivially_constructible
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

// Declare structures
struct X {
};

struct Y {

    // Default Constructor
    Y() {}

    // Parameterized Constructor
    Y(const X&)
    noexcept {}
};

// Driver Code
int main()
{
    cout << boolalpha;

    // Check if int is a trivally
    // constructible or not
    cout << "int(): "
         << is_trivially_constructible<int>::value
         << endl;

    // Check if struct Y is a trivally
    // constructible or not
    cout << "Y(): "
         << is_trivially_constructible<Y>::value
         << endl;

    // Check if Y(X) is a trivally
    // constructible or not
    cout << "Y(X): "
         << is_trivially_constructible<Y, X>::value
         << endl;

    return 0;
}

Output:

int(): true
Y(): false
Y(X): false

Reference: http://www.cplusplus.com/reference/type_traits/is_trivially_constructible/