boost::type_traits::is_array Template in C++

Last Updated : 30 Mar, 2020

The std::boost::is_array template of Boost C++ Library used to check whether the given type is an array type or not. It returns a boolean value showing the same.

Header Files:

#include "boost/type_traits/is_array.hpp" 
or 
#include "boost/type_traits.hpp"

Template Class:

template <class T>
struct is_array : public true_type-or-false_type {};

If T is an array type then inherits from true_type else inherits from false_type.

Syntax:

boost::integral_constant ::value
boost::integral_constant ::value_type
boost::integral_constant ::type

Parameter: This template accepts a single parameter T(Trait class) to check whether T is a pointer type or not.

Accepted Arguments:

typename T
volatile T []
const volatile T []
const T []
T []
const volatile T[N]
volatile T [N]
const T [N]
T [N]

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

True: If the type is a pointer value.
False: If the type is a not pointer value.

Below programs illustrate the std::boost::type_traits::is_array template:
Program 1:

// C++ program to illustrate std::is_array template 
#include <bits/stdc++.h> 
#include <boost/type_traits/is_array.hpp> 
#include <boost/typeof/typeof.hpp> 
using namespace std; 
  
// Main Program 
int main() 
{ 
    cout << "is_array: \n"; 
    cout << "int[]: "
         << boost::is_array<int[]>::value 
         << "\n"; 
    cout << "char[]: "
         << "boost::is_array<char[]>::value"
         << "\n"; 
  
    cout << "double[20]: "
         << boost::is_array<double[20]>::value 
         << "\n"; 
    cout << "float[30]: "
         << boost::is_array<float[30]>::value 
         << "\n"; 
  
    cout << "bool[][6]: "
         << boost::is_array<bool[][6]>::value 
         << "\n"; 
    cout << "long[56][34][98]: "
         << boost::is_array<long[56][34][98]>::value 
         << "\n"; 
  
    bool a[98]; 
  
    cout << "bool a[98]: "
         << boost::is_array<decltype(a)>::value 
         << "\n"; 
  
    char c[0]; 
  
    cout << "char c[0]: "
         << boost::is_array<decltype(c)>::value 
         << "\n"; 
  
    return 0; 
} 

Output:

is_array: 
int[]: 1
char[]: boost::is_array::value
double[20]: 1
float[30]: 1
bool[][6]: 1
long[56][34][98]: 1
bool a[98]: 1
char c[0]: 0

Program 2:

// C++ program to illustrate std::is_array template 
#include <bits/stdc++.h> 
#include <boost/type_traits/is_array.hpp> 
#include <boost/typeof/typeof.hpp> 
using namespace std; 
  
// A Structure 
struct sturec { 
    int x, y; 
    float a, b; 
    long t[90]; 
}; 
  
// A Class 
class student { 
private: 
    string name; 
    int roll_no; 
  
public: 
    student(string name, int roll_no); 
    string studentName(int roll_no); 
}; 
  
// Parameterized Constructor 
student::student(string name, int roll_no) 
{ 
    this->name = name; 
    this->roll_no = roll_no; 
} 
  
// Function that return the name 
// of the student 
string student::studentName(int roll_no) 
{ 
    return this->name; 
} 
  
// Main Program 
int main() 
{ 
    cout << "is_array: \n"; 
  
    sturec s; 
    sturec p[3]; 
  
    cout << "instance of structure: "
         << boost::is_array<decltype(s)>::value 
         << "\n"; 
    cout << "array of structure: "
         << boost::is_array<decltype(p)>::value 
         << "\n"; 
  
    // Instance of Class 
    student S("GeeksforGeeks", 11840520); 
    cout << "instance of a class: "
         << boost::is_array<decltype(S)>::value 
         << "\n"; 
  
    // Array of Class 
    student a[3] = { 
        { "Abc Def", 11840820 }, 
        { "Xyz Xyz", 11840220 }, 
        { "ABcd Gfgh", 11840950 } 
    }; 
  
    cout << "array of a class: "
         << boost::is_array<decltype(a)>::value 
         << "\n"; 
  
    return 0; 
} 

Output:

is_array: 
instance of structure: 0
array of structure: 1
instance of a class: 0
array of a class: 1

<type_traits> Header in C++

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