The is_pointer template of Boost library is used to check whether the given type is a pointer or not. It returns a boolean value showing the same.
Header Files:
#include "boost/type_traits.hpp" or #include "boost/type_traits/is_pointer.hpp"
Template Class:
template <class T> struct is_pointer : public true_type-or-false_type {};
If T is a pointer type then inherits from true_type else inherits from false_type.
Syntax:
boost::is_pointer::value boost::is_pointer::value_type
Parameter: This template accepts a single parameter T(Trait class) to check whether T is a pointer type or not.
Accepted Arguments: This template accept the below arguments:
typename T T *volatile T *const volatile T *const T *
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 illustrates the std::is_pointer template in C++ STL:
Program 1:
// C++ program to illustrate // std::is_floating_point template #include <bits/stdc++.h> #include <boost/type_traits/is_pointer.hpp> #include <boost/typeof/typeof.hpp> using namespace std;
// Main Program int main()
{ cout << "is_pointer_type: \n" ;
cout << "int *: "
<< boost::is_pointer< int *>::value << "\n" ;
cout << "char *: "
<< boost::is_pointer< char *>::value
<< "\n" ;
// Pointer to integer
int * a;
cout << "pointer to integer: "
<< boost::is_pointer< decltype (a)>::value
<< "\n" ;
// Pointer to 1D array
int * b = new int [29];
cout << "pointer to 1-D array: "
<< boost::is_pointer< decltype (b)>::value
<< "\n" ;
// 1-D array
int c[20];
cout << "1-D array :"
<< boost::is_pointer< decltype (c)>::value
<< "\n" ;
return 0;
} |
is_pointer_type: int *: 1 char *: 1 pointer to integer: 1 pointer to 1-D array: 1 1-D array :0
Program 2:
// C++ program to illustrate // std::is_floating_point template #include <bits/stdc++.h> #include <boost/type_traits/is_pointer.hpp> #include <boost/typeof/typeof.hpp> using namespace std;
// Function with an integer // argument and void return type void fun( int x)
{ cout << "value of x is : " << x << "\n" ;
} // A Structure struct A {
int x;
char a[8];
}; // A Class class student {
int roll;
string name;
public :
// Student Class Constructor
student( int x, string y)
{
roll = x;
name = y;
}
// Member function to get the
// name of a student
string get_name()
{
return name;
}
// Member function to get the
// roll number of a student
int get_roll()
{
return roll;
}
}; // Main Program int main()
{ cout << "is_pointer_type: \n" ;
// Pointer to function
void (*ptr)( int ) = &fun;
cout << "pointer to fun: "
<< boost::is_pointer< decltype (ptr)>::value
<< "\n" ;
// Instance of A
A obj;
cout << "instance of a structure: "
<< boost::is_pointer< decltype (obj)>::value
<< "\n" ;
// Pointer to instance of A
A* obj2;
cout << "pointer to instance of a structure: "
<< boost::is_pointer< decltype (obj2)>::value
<< "\n" ;
// Instance of student
student s(11840220, "GeeksforGeeks" );
cout << "instance of a class: "
<< boost::is_pointer< decltype (s)>::value
<< "\n" ;
// Pointer to instance of student
student* S;
S = &s;
cout << "pointer to instance of a class: "
<< boost::is_pointer< decltype (S)>::value
<< "\n" ;
return 0;
} |
is_pointer_type: pointer to fun: 1 instance of a structure: 0 pointer to instance of a structure: 1 instance of a class: 0 pointer to instance of a class: 1