The std::is_const template of C++ STL is used to check whether the type is a const-qualified or not. It returns a boolean value showing the same.
Syntax:
template < class T >struct is_const;
Template Parameter: This template contains single parameter T (Trait class) to check whether T is a const-qualified type.
Return Value: This template returns a boolean value as shown below:
- True: if the type is a const-qualified.
- False: if the type is a non-const-qualified.
Below programs illustrate the is_const template in C++ STL:
Program 1:
// C++ program to illustrate // is_const #include <iostream> #include <type_traits> using namespace std;
// main program int main()
{ cout << boolalpha;
cout << "is_const:"
<< endl;
cout << "int:"
<< is_const< int >::value
<< '\n' ;
cout << "const int:"
<< is_const< const int >::value
<< '\n' ;
cout << "const int&:"
<< is_const< typename remove_reference< const int &>::type>::value
<< '\n' ;
return 0;
} |
Output:
is_const: int:false const int:true const int&:true
Program 2:
// C++ program to illustrate // is_const #include <iostream> #include <type_traits> using namespace std;
// main program int main()
{ cout << boolalpha;
cout << "is_const:"
<< endl;
cout << "const int*:"
<< is_const< const int *>::value
<< '\n' ;
cout << "int* const:"
<< is_const< int * const >::value
<< '\n' ;
cout << "const int&:"
<< is_const< const int &>::value
<< '\n' ;
return 0;
} |
Output:
is_const: const int*:false int* const:true const int&:false
Program 3:
// C++ program to illustrate // is_const #include <iostream> #include <type_traits> using namespace std;
// main program int main()
{ cout << boolalpha;
cout << "is_const:"
<< endl;
cout << "float:"
<< is_const< float >::value
<< '\n' ;
cout << "const float:"
<< is_const< const float >::value
<< '\n' ;
cout << "char const:"
<< is_const< char const >::value
<< '\n' ;
cout << "double:"
<< is_const< double >::value
<< '\n' ;
return 0;
} |
Output:
is_const: float:false const float:true char const:true double:false