set::empty and set::clear

Illustrates how to use the set::empty and set::clear Standard Template Library (STL) functions in Visual C++.

template<class _K, class _Pr, class _A>
   class set
   {
      public:
      // Function 1:
      bool empty() const;
      // Function 2:
      void clear();
   }

Remarks

注意

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

The empty function returns true when there are no elements in the controlled sequence. By calling erase(begin, end), the clear function removes all elements in the controlled sequence. For more information on the erase function, see set::erase.

Example

// SetEmptyClear.cpp
// compile with: /EHsc
//
//      Illustrates how to use the empty function to determine if
//      there are elements in the controlled sequence. It also
//      illustrates how to use the clear function to remove all
//      elements from the controlled sequence.
//
// Functions:
//
//    empty        Returns true if there are no elements in the
//                 controlled sequence.
//    clear        Removes all elements from the controlled sequence.
//////////////////////////////////////////////////////////////////////

#pragma warning(disable:4786)
#include <set>
#include <iostream>

using namespace std ;

typedef set<int> SET_INT;

void truefalse(int x)
{
  cout << (x?"True":"False") << endl;
}

int main() {
  SET_INT s1;

  cout << "s1.empty() returned ";
  truefalse(s1.empty());  // True

  cout << "s1.insert(5)" << endl;
  s1.insert(5);
  cout << "s1.insert(8)" << endl;
  s1.insert(8);

  cout << "s1.empty() returned ";
  truefalse(s1.empty());  // False

  cout << "s1.clear()" << endl;
  s1.clear();

  cout << "s1.empty() returned ";
  truefalse(s1.empty());  // True
}

Output

s1.empty() returned True
s1.insert(5)
s1.insert(8)
s1.empty() returned False
s1.clear()
s1.empty() returned True

Requirements

Header: <set>

See Also

Concepts

Standard Template Library Samples