The std::is_empty template of C++ STL is used to check whether the given type is empty or not. This method returns a boolean value showing whether the given type is empty or not.
Syntax:
template < class T > struct is_empty;
Parameters: This template contains single parameter T (Trait class) that identifies whether T is a empty type.
Return Value: This template returns a boolean value as shown below:
- True: if the type is a empty.
- False: if the type is not empty.
Below programs illustrate the std::is_empty template in C++ STL:
Program 1: Using Structs
// C++ program to illustrate // std::is_empty template #include <iostream> #include <type_traits> using namespace std;
// empty struct struct GFG1 {
}; // struct with local variable struct GFG2 {
int variab;
}; // Struct with global variable struct GFG3 {
static int variab;
}; // Struct with virtual destructor struct GFG4 {
virtual ~GFG4();
}; // Driver code int main()
{ cout << boolalpha;
cout << "Is GFG1 empty: "
<< is_empty<GFG1>::value
<< '\n' ;
cout << "Is GFG2 empty: "
<< is_empty<GFG2>::value
<< '\n' ;
cout << "Is GFG3 empty: "
<< is_empty<GFG3>::value
<< '\n' ;
cout << "Is GFG4 empty: "
<< is_empty<GFG4>::value
<< '\n' ;
return 0;
} |
Output:
Is GFG1 empty: true Is GFG2 empty: false Is GFG3 empty: true Is GFG4 empty: false
Program 2: Using classes
// C++ program to illustrate // std::is_empty template #include <iostream> #include <type_traits> using namespace std;
// empty class class GFG1 {
}; // class with local variable class GFG2 {
int variab;
}; // class with global variable class GFG3 {
static int variab;
}; // class with virtual destructor class GFG4 {
virtual ~GFG4();
}; int main()
{ cout << boolalpha;
cout << "Is GFG1 empty: "
<< is_empty<GFG1>::value
<< '\n' ;
cout << "Is GFG2 empty: "
<< is_empty<GFG2>::value
<< '\n' ;
cout << "Is GFG3 empty: "
<< is_empty<GFG3>::value
<< '\n' ;
cout << "Is GFG4 empty: "
<< is_empty<GFG4>::value
<< '\n' ;
return 0;
} |
Output:
Is GFG1 empty: true Is GFG2 empty: false Is GFG3 empty: true Is GFG4 empty: false