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is_const Template in C++
In this article we will be discussing the working, syntax and examples of std::is_const template in C++ STL.
is_const template in C++ is used to check whether the defined type is a const-qualified type or not.
What is const-qualified type?
We say a type as a const-qualified when the value of the type is constant. Constant data type is a type in which once a value is initialised in a const can’t be changed or altered throughout the program.
Syntax
template <class T> is_const;
Parameters
The template can have only parameter of type T, and check whether the given type is a constqualifier or not
Return value
It returns a Boolean value, true if the given type is a const-qualifier, and false if the given type is not a const-qualifier.
Example
Input: is_const<const int>::value; Output: True Input: is_const<int>::value; Output: False
Example
#include <iostream>
#include <type_traits>
using namespace std;
int main() {
cout << boolalpha;
cout << "checking for is_const template: ";
cout << "\nInt : "<<is_const<int>::value;
cout << "\nConst int : "<< is_const<const int>::value;
cout << "\nConst int& : "<< is_const<const int&>::value;
return 0;
}Output
If we run the above code it will generate the following output −
checking for is_const template: Int : false Const int : true Const int& : false
Example
#include <iostream>
#include <type_traits>
using namespace std;
int main() {
cout << boolalpha;
cout << "checking for is_const template: ";
cout << "\nFloat : "<<is_const<float>::value;
cout << "\nChar : "<<is_const<char>::value;
cout << "\nFloat *: "<<is_const<float*>::value;
cout << "\nChar *: "<<is_const<char*>::value;
cout << "\nConst int* : "<< is_const<const int*>::value;
cout << "\nint* const : "<< is_const<int* const>::value;
return 0;
}Output
If we run the above code it will generate the following output −
checking for is_const template: Float : false Char: false Float *: false Char *: fakse Const int* : false int* const: true
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