is_const Template in C++
Last Updated :
19 Nov, 2018
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:
#include <iostream>
#include <type_traits>
using namespace std;
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:
#include <iostream>
#include <type_traits>
using namespace std;
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:
#include <iostream>
#include <type_traits>
using namespace std;
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
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